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PROFESSOR: OK, let's
get started.

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Everyone can go ahead and take
10 more seconds on today's

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clicker question.

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This is about hybridization,
which we will go over more to

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start today, but just
to see where we are

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as a starting point.

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All right, great.

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So most of you got this.

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The question is what was the
hybridization of an atom if we

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know that it has two
hybrid orbitals.

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This is really, really
important, so I'm just going

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to write this out for that 20%
of you that didn't see this

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right away.

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00:00:54,870 --> 00:00:57,700
So we know that when we have
hybrid orbitals that come from

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s and p orbitals, these are our
atomic orbitals we have to

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choose from to hybridize.

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00:01:03,420 --> 00:01:06,420
So if we know, for example,
that we need two hybrid

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orbitals, that means we needed
to have started with two

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atomic orbitals.

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So that means what we would
form are two s p hybrid

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orbitals and we'd be left
with our other two p

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orbitals left over.

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So any time you figure out that
you're going to need two

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hybrid orbitals, and we'll go
over when you would find this

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out in just a minute, but any
time that happens you know it

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has to come from an s and a p,
so that's why you'll end up

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00:01:30,980 --> 00:01:33,620
with s p hybrid orbitals
there.

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And exam 2 is happening in just
one week from today, so

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next Wednesday.

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The semester moves really fast.
So I can't believe we're

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already up to exam 2
talk, but we are.

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00:01:43,550 --> 00:01:47,060
So, you should have all received
two handouts when you

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walked in today, your notes and
then an exam 2 info sheet.

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Did everybody get that?

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If you didn't get it, just raise
your hand and a TA will

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come to you with that.

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I see there's a few around, if
one of the TA's can jump up

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and fill those in.

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All right, so basically,
as with exam 1, all the

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information you need to know
about what's going to be on

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exam 2 is on this handout.

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Specifically exam 2
is going to cover

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lectures 10 through 17.

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Today is lecture 16, so that
means it's going to cover

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today's lecture and then a bit
into Friday's lecture as well,

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so I'll be really clear on
Friday where exam 2 material

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ends, where you can kind of
switch off the exam 2 part of

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your studying.

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And it will also be on
problem-sets 4 and 5.

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So it's going to be on two
problem-sets instead of three

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problem-sets, but as you know,
there are a lot of different

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concepts covered in these
two problem-sets.

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So it's still a lot to be
thinking about and you need to

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make sure that you really
understand all of these

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different concepts.

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So this is explicitly listed
in this sheet here, so make

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sure you look it over.

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But I just want to say is well,
the concepts that we've

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covered since exam 1 have been
talking about covalent bonds,

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going along with that are all
the Lewis structures that

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we've done.

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Then we talked about ionic
bonds, so you need to make

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sure you can solve those ionic
bond problems. And then we

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started talking about different
types of bonding in

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terms of thinking about MO
theory, and also vesper theory

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and hybridization.

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And then today, and a little
bit on Friday, you'll be

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responsible for some of this new
material, which is going

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to be a little bit of
thermochemistry.

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Not too much on exam 2, most of
that will be saved for exam

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3 material, but an intro to
thermochemistry, that will

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also be on the exam, just as
far as these two lectures.

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So, basically this is all
written out here, and I also

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want to mention in terms of
your MO diagrams and MO

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theory, I sent out an email
about this, but I also wrote

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it out here so you have it
written down in terms of what

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you are responsible for in terms
of ordering the energy

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levels of molecular orbitals.

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So that's all written down
explicitly right here, this is

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what you need to know
for the exam.

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Also it's helpful for the
problem-set as well.

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And also, in terms of MO
diagrams, I think that you

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will already gone over this
pretty explicitly either last

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week in recitation or yesterday,
in terms of what

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you need to do to get full
credit when you're actually

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00:04:08,120 --> 00:04:09,850
drawing an MO diagram.

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00:04:09,850 --> 00:04:12,300
Just in case you don't have that
information or you didn't

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00:04:12,300 --> 00:04:15,240
write it down, I wrote this down
for you here as well in

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terms of things like making
sure to draw your energy

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arrows, or remembering
to label all

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of your atomic orbitals.

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We don't want anyone getting
points off on the exam for

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doing something silly where
they do understand what's

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going on, but they're
just not writing it

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in the correct form.

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So all this information
is on your sheet here.

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00:04:31,240 --> 00:04:33,650
And also on this sheet mentions
that you will be

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getting optional extra
problems on Friday.

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This is just like for exam 1.

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The way that you should approach
these extra problems,

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you don't need to turn them in,
you're not required to do

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them, but if you want to do well
on the exam we really,

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really encourage that you do
these problems. And in terms

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of having it be worth your time
when you're solving these

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00:04:52,330 --> 00:04:54,430
problems, what you want to do
is make sure you're at the

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point where you can put your
notes away, where you can sit

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alone without your friends,
and really approach these

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extra problems as if they're
exam problems. This way if

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00:05:02,460 --> 00:05:05,050
there's some conceptual leap
that you haven't quite made

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yet, but you don't realize it
because you've been using your

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notes or using the conversations
with your

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00:05:09,830 --> 00:05:12,960
friends, you want to make that
leap and run into those

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problems alone in your room
when you have two hours to

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figure it out.

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00:05:16,860 --> 00:05:19,140
You don't want to do this
leap on an exam.

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That's not the ideal
situation.

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00:05:20,970 --> 00:05:23,170
So especially with Lewis
structures where sometimes you

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can run into confusions that you
need to work through and

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00:05:25,520 --> 00:05:27,870
make sure it all makes sense in
terms of your head how to

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do this, make sure you take the
time to do that before the

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exam and don't have to end up
struggling with that on the

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exam in a time situation.

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All right, so the extra problem
solutions will be

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posted on Sunday.

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And in terms of office hours for
next week, my office hours

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are going to be on Monday from
2 to 4, I'm moving them up,

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and your TAs will move up their
office hours as well, so

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check with them in recitation
or on the website.

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So that's pretty much
it for exam 2.

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Are there any questions about
what you're responsible for or

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anything regarding exam 2?

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00:06:05,220 --> 00:06:07,740
OK, and in terms of the room
it's in Walker again, so at

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00:06:07,740 --> 00:06:09,150
least this part should
be familiar.

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You'll be used to going to your
row, it'll be the same

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00:06:11,500 --> 00:06:14,090
row, it's all written here
again, but you can just do

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exactly what you
did for exam 1.

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All right, so one last class
announcement, and this is that

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if you've been looking at our
first sheet of the whole year,

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sort of the course overview
sheet, you know that our class

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00:06:26,960 --> 00:06:30,980
in terms of grading is out of
750 points, and 50 of those

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points are for attendance and
something called occasional

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in-class quizzes.

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So what we're going to do is
start filling in some of those

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00:06:38,400 --> 00:06:41,990
points because we only have 36
classes worth of attendance.

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So we have a couple of points
to make up in terms of

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quizzes, and these are going to
be clicker quizzes, and let

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00:06:47,170 --> 00:06:48,980
me explain how this
is going to work.

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Basically, in at least for my
part of the class, what we're

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going to do, because what I
really care about is that

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people are answering the clicker
questions, it's really

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valuable for me.

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I don't necessarily care if you
get them right or wrong

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during class, because this is
the point at which you're

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still learning them.

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So these quiz points, which
could be up to 2 points per

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class, will be in addition to
attendance points, and you'll

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get full credit if you answer
the quiz question.

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So you need to be answering
the questions because the

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00:07:17,100 --> 00:07:18,630
quizzes will not be announced.

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So this is another reward for
people that are always

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00:07:21,330 --> 00:07:22,410
participating.

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These clicker questions are
really valuable to us in terms

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of the feedback, it really gives
me an idea of where the

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class is as a whole.

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So really, it's important that
you are answering these

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questions and this is a way to
get your quiz points up, so in

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addition to attendance, you'll
get 2 quiz points.

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We'll have our first unannounced
quiz today, so you

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won't know what problem it is
beforehand, so I suggest you

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make sure you're answering all
the clicker questions, which

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most of you do anyway.

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And I will just say I recognize
that some of you are

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just scurrying across campus
to get here on time.

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So I'll never make that first
question a quiz question,

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because I know how hard it is
to get from one place to

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another on this campus, and I
know most of you do a great

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00:08:01,280 --> 00:08:04,280
job of sneaking in right at the
last minute when you have

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that long run.

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00:08:04,890 --> 00:08:07,390
So we won't make the first
question a quiz question, but

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be on the look out for a
quiz question today.

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All right.

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So let's get to today's topic.

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We're going to finish talking
about valence bond theory and

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hybridization.

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So what we've already done is
really cover all the theory

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that we're going to cover
behind how hybridization

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works, and behind how valence
bond theory works.

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But what we haven't covered is
how do we actually solve

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problems doing this in
the really quick way.

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So we're going to do that.

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This is going to be a more
practical lesson in

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hybridization.

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And once we do that, we'll move
on to now talking about

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energies and enthalpies
of chemical reactions.

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So this is a real shift.

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We spent a while talking about
single atoms, and then we've

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spent most of the material,
since exam 1,

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talking about bonding.

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So now we're taking it one step
further and we're going

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to actually get to talk about
some chemical reactions.

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So we'll do that once we
finish up with our

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hybridization unit here.

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All right, so how do we
go about determining

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hybridization in complex
molecules?

212
00:09:07,140 --> 00:09:10,780
It's actually incredibly simple,
and all that you need

213
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to do is think about for the
given atom that you're looking

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00:09:13,930 --> 00:09:17,230
at, what you want to do is add
up the number of atoms that

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00:09:17,230 --> 00:09:19,460
are bonded to your central
atom, or the atom you're

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considering, and add to that
the number of lone pairs.

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00:09:23,260 --> 00:09:25,710
And what you end up with is the
number of hybrid orbitals

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that you need.

219
00:09:26,650 --> 00:09:29,760
All right, so the theory behind
hybridization and

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00:09:29,760 --> 00:09:31,910
picturing everything, that can
be pretty complicated, and I

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00:09:31,910 --> 00:09:33,470
do want you to understand
that.

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00:09:33,470 --> 00:09:36,630
But if, for example, on an
exam situation, you don't

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necessarily have to think
through everything, you can

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00:09:38,520 --> 00:09:40,930
just use this very quick way
to figure out the number of

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00:09:40,930 --> 00:09:42,830
hybrid orbitals that you need.

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And what we just said is that
any time we need two hybrid

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orbitals, we know that the
hybridization of that atom is

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going to be s p, because
it's made up of

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one s and one p orbital.

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So let's say we need three
hybrid orbitals.

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00:10:02,140 --> 00:10:06,910
What is our hybridization of
our atom in this case?

232
00:10:06,910 --> 00:10:09,440
Yeah, it's s p 2.

233
00:10:09,440 --> 00:10:14,100
We want to take three atomic
orbitals to make three hybrid

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00:10:14,100 --> 00:10:16,720
orbitals, so it's going
to be s p 2.

235
00:10:16,720 --> 00:10:19,290
So what if we need four hybrid
orbitals, what's the

236
00:10:19,290 --> 00:10:20,940
hybridization going to
be in this case?

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00:10:20,940 --> 00:10:23,240
STUDENT: S p 3.

238
00:10:23,240 --> 00:10:25,440
PROFESSOR: S p 3.

239
00:10:25,440 --> 00:10:25,890
All right, great.

240
00:10:25,890 --> 00:10:26,360
So, really that's it.

241
00:10:26,360 --> 00:10:29,450
Hopefully hybridization just got
a lot simpler for any of

242
00:10:29,450 --> 00:10:31,810
you that have been struggling
a little bit with it.

243
00:10:31,810 --> 00:10:34,700
But let's go ahead and do an
example to make sure that we

244
00:10:34,700 --> 00:10:35,970
can all do this.

245
00:10:35,970 --> 00:10:38,450
And let's take a look --
first let me mention

246
00:10:38,450 --> 00:10:39,810
an exception here.

247
00:10:39,810 --> 00:10:43,900
The one exception to thinking
about how many hybrid orbitals

248
00:10:43,900 --> 00:10:47,300
that you have are in the case
where you have single bonded

249
00:10:47,300 --> 00:10:51,150
terminal atoms. So in the case
of a terminal atom that is a

250
00:10:51,150 --> 00:10:53,730
single bond, you're not
going to hybridize it.

251
00:10:53,730 --> 00:10:56,500
So in that case, just don't even
change anything it's just

252
00:10:56,500 --> 00:10:58,630
going to be one of the p
orbitals, or unless you're

253
00:10:58,630 --> 00:11:00,900
talking about hydrogen in
which case will be an s

254
00:11:00,900 --> 00:11:02,890
orbital that overlaps.

255
00:11:02,890 --> 00:11:05,520
All right, so we can illustrate
this with an

256
00:11:05,520 --> 00:11:08,250
example of formal chloride.

257
00:11:08,250 --> 00:11:10,600
So this is a good example
because we're just dealing

258
00:11:10,600 --> 00:11:14,110
with our carbon as our central
atom here, and we have three

259
00:11:14,110 --> 00:11:17,750
terminal atoms, two of which
are single bonded, so we're

260
00:11:17,750 --> 00:11:21,800
not going to hybridize those,
and one which is double

261
00:11:21,800 --> 00:11:25,100
bonded, the oxygen, so we
will hybridize that one.

262
00:11:25,100 --> 00:11:27,540
So in terms of thinking about
the carbon, what is a

263
00:11:27,540 --> 00:11:29,560
hybridization around
the carbon atom?

264
00:11:29,560 --> 00:11:34,730
STUDENT: [INAUDIBLE]

265
00:11:34,730 --> 00:11:36,360
PROFESSOR: All right, I'm
hearing some mixed answers.

266
00:11:36,360 --> 00:11:37,070
So let's think.

267
00:11:37,070 --> 00:11:41,570
So the carbon atom is bonded to
three different atoms, and

268
00:11:41,570 --> 00:11:43,090
it has no lone pairs.

269
00:11:43,090 --> 00:11:43,870
So what's the hybridization?

270
00:11:43,870 --> 00:11:46,570
STUDENT: S p 2.

271
00:11:46,570 --> 00:11:47,890
PROFESSOR: Good s p 2.

272
00:11:47,890 --> 00:11:50,430
So, if we're talking about the
c h bond, we're going to say

273
00:11:50,430 --> 00:11:54,240
that it's carbon, it's a sigma
bond because it's a single

274
00:11:54,240 --> 00:11:57,600
bond, and then it's carbon
2 s p 2 bonded to a

275
00:11:57,600 --> 00:11:59,080
hydrogen 1 s orbital.

276
00:11:59,080 --> 00:12:02,060
All right, so let's take
a look at the carbon

277
00:12:02,060 --> 00:12:03,660
chlorine bond here.

278
00:12:03,660 --> 00:12:08,850
Again, carbon is still 2 s p 2,
it's the same carbon atom,

279
00:12:08,850 --> 00:12:11,420
and it's going to be a sigma
bond because it's a single

280
00:12:11,420 --> 00:12:14,120
bond, but what about the
chlorine, what atomic orbital

281
00:12:14,120 --> 00:12:15,890
is going to be bonding
in the chlorine?

282
00:12:15,890 --> 00:12:16,526
STUDENT: [INAUDIBLE]

283
00:12:16,526 --> 00:12:17,480
PROFESSOR: All right.

284
00:12:17,480 --> 00:12:21,670
I'm hearing a little bit of
mixes, they're all p's, which

285
00:12:21,670 --> 00:12:22,730
is a good start.

286
00:12:22,730 --> 00:12:26,780
It turns out that it's going
to be the chlorine 3 p z.

287
00:12:26,780 --> 00:12:29,570
So the reason that it's p is
because we're not hybridizing

288
00:12:29,570 --> 00:12:32,990
it, and the reason that I
specifically say that it's the

289
00:12:32,990 --> 00:12:36,760
p z instead of the p x or the
p y, is remember that the

290
00:12:36,760 --> 00:12:39,960
z-axis, that's our bonding
axis, that's our

291
00:12:39,960 --> 00:12:41,270
internuclear axis.

292
00:12:41,270 --> 00:12:44,280
So any time we have a p orbital
that's involved in a

293
00:12:44,280 --> 00:12:47,510
sigma bond, it has to be the z
orbital because that's the

294
00:12:47,510 --> 00:12:50,570
only one that has the right
orientation to overlap along

295
00:12:50,570 --> 00:12:52,090
that z-axis.

296
00:12:52,090 --> 00:12:55,940
So we're going to say it's
carbon s p 2, and then

297
00:12:55,940 --> 00:12:57,700
chlorine 3 p z.

298
00:12:57,700 --> 00:13:02,850
All right, so let's look at the
last bond here, which is a

299
00:13:02,850 --> 00:13:04,980
carbon oxygen double bond.

300
00:13:04,980 --> 00:13:07,760
We know that any time we have a
double bond it's made up of

301
00:13:07,760 --> 00:13:10,910
one sigma bond plus
one pi bond.

302
00:13:10,910 --> 00:13:14,710
So, when we look at the carbon
again, that's 2 s p 2.

303
00:13:14,710 --> 00:13:17,170
But what about the oxygen,
what's the hybridization of

304
00:13:17,170 --> 00:13:20,490
this oxygen atom?

305
00:13:20,490 --> 00:13:22,790
S p 2.

306
00:13:22,790 --> 00:13:26,270
So we're going to have carbon
2 s p 2, and then

307
00:13:26,270 --> 00:13:28,060
oxygen 2 s p 2.

308
00:13:28,060 --> 00:13:32,590
It's s p 2 because the oxygen is
bonded to one atom plus two

309
00:13:32,590 --> 00:13:34,000
lone pairs, so we're going
to have a total of

310
00:13:34,000 --> 00:13:35,060
three hybrid orbitals.

311
00:13:35,060 --> 00:13:38,260
All right, so this is not our
only bond, we have a double

312
00:13:38,260 --> 00:13:40,990
bond, so we also need to
talk about the pi bond.

313
00:13:40,990 --> 00:13:44,270
So if we talk about the pi bond,
we can say that's carbon

314
00:13:44,270 --> 00:13:47,100
2 p y, then the oxygen 2 p y.

315
00:13:47,100 --> 00:13:49,910
We could alternatively say, and
be correct, that it was

316
00:13:49,910 --> 00:13:52,840
the carbon 2 p x and
the oxygen 2 p x.

317
00:13:52,840 --> 00:13:54,240
Either one of those is fine.

318
00:13:54,240 --> 00:13:57,920
All right, so that's an example
of how we can assign

319
00:13:57,920 --> 00:14:01,000
very quickly and very easily
what the hybridization is of a

320
00:14:01,000 --> 00:14:02,290
given atom.

321
00:14:02,290 --> 00:14:05,890
And then also fully describe the
symmetry and the atomic or

322
00:14:05,890 --> 00:14:08,120
hybrid orbitals that
make up bonds.

323
00:14:08,120 --> 00:14:10,600
So this is a lot of your
problems on the p-set, so if

324
00:14:10,600 --> 00:14:12,700
you haven't finished that
section, hopefully you'll be

325
00:14:12,700 --> 00:14:15,260
able to get through that section
pretty quickly when

326
00:14:15,260 --> 00:14:16,470
you go back to it.

327
00:14:16,470 --> 00:14:19,650
And let's take a look at a
little bit of a more complex

328
00:14:19,650 --> 00:14:23,040
molecule here, which is ascorbic
acid or vitamin C.

329
00:14:23,040 --> 00:14:25,740
And this is a good example
because it's starting to look

330
00:14:25,740 --> 00:14:28,910
a little more complicated, but
not too much more complicated.

331
00:14:28,910 --> 00:14:32,070
But the reality is if you know
how to do assigning the

332
00:14:32,070 --> 00:14:35,950
hybridization this way, even
if I gave you a 1,000 atom

333
00:14:35,950 --> 00:14:37,420
protein, you should still
be able to get

334
00:14:37,420 --> 00:14:39,330
it completely correct.

335
00:14:39,330 --> 00:14:42,280
Vitamin C is a really important
molecule to actually

336
00:14:42,280 --> 00:14:44,780
think about in terms of thinking
about its shape and

337
00:14:44,780 --> 00:14:45,260
its hybridization.

338
00:14:45,260 --> 00:14:48,180
Vitamin C is an antoxidant.

339
00:14:48,180 --> 00:14:50,780
So we might remember that from
when we were talking about

340
00:14:50,780 --> 00:14:52,040
free radicals.

341
00:14:52,040 --> 00:14:54,450
Free radicals can cause
oxidative damage.

342
00:14:54,450 --> 00:14:57,080
These antioxidants, some of
our vitamins, including

343
00:14:57,080 --> 00:14:59,300
vitamin C are antioxidants.

344
00:14:59,300 --> 00:15:01,500
So that's something that a lot
of people in the general

345
00:15:01,500 --> 00:15:04,760
population know if they're
into their health.

346
00:15:04,760 --> 00:15:07,960
But another really important
thing about ascorbic acid is

347
00:15:07,960 --> 00:15:10,870
that it's an enzyme cofactor.

348
00:15:10,870 --> 00:15:15,160
And a cofactor just means that
it's some type of molecule or

349
00:15:15,160 --> 00:15:18,070
atom, in this case it's a
molecule, that's required by

350
00:15:18,070 --> 00:15:19,990
an enzyme in order
for the enzyme to

351
00:15:19,990 --> 00:15:21,670
carry out its chemistry.

352
00:15:21,670 --> 00:15:24,990
And the chemistry that the
enzymes that vitamin C are a

353
00:15:24,990 --> 00:15:28,700
cofactor for are responsible
for putting oxygen, o h

354
00:15:28,700 --> 00:15:32,350
groups, onto collagen molecules
in order to form

355
00:15:32,350 --> 00:15:35,100
what is the collagen
triple helix.

356
00:15:35,100 --> 00:15:38,790
And collagen is the main
constituent of bones, of

357
00:15:38,790 --> 00:15:44,070
joints, of connective tissue,
of many important structural

358
00:15:44,070 --> 00:15:45,140
parts of our bodies.

359
00:15:45,140 --> 00:15:47,700
So you can imagine that vitamin
C is very important

360
00:15:47,700 --> 00:15:49,960
because we need to keep
our collagen intact.

361
00:15:49,960 --> 00:15:52,460
Collogen is actually one of the
most prevalent proteins in

362
00:15:52,460 --> 00:15:56,790
our entire body, and it makes up
a large part of our cells.

363
00:15:56,790 --> 00:15:59,960
So you can imagine if we don't
have collagen that is in this

364
00:15:59,960 --> 00:16:02,910
triple helix, we're going to run
into some problems. Does

365
00:16:02,910 --> 00:16:05,430
anyone, or I'm sure many of you
do know, but can someone

366
00:16:05,430 --> 00:16:07,840
tell me what the name is of
the disease if you have a

367
00:16:07,840 --> 00:16:09,410
deficiency in vitamin C?

368
00:16:09,410 --> 00:16:10,560
STUDENT: Scurvy.

369
00:16:10,560 --> 00:16:12,630
PROFESSOR: Yeah, scurvy.

370
00:16:12,630 --> 00:16:17,330
So scurvy, most often associated
with ships because

371
00:16:17,330 --> 00:16:23,400
of the 1500's and 1600's and
1700's when boating technology

372
00:16:23,400 --> 00:16:27,330
was far above biochemistry
technology, so people could

373
00:16:27,330 --> 00:16:29,890
make ships and go on these long
journeys, but people did

374
00:16:29,890 --> 00:16:33,190
not yet understand they needed
to keep certain vitamins in

375
00:16:33,190 --> 00:16:36,720
their bodies, such as vitamin
C. Maybe also, they didn't

376
00:16:36,720 --> 00:16:38,690
know about -- well they didn't
even have the structure, so

377
00:16:38,690 --> 00:16:41,390
they couldn't have realized that
vitamin C is polar and

378
00:16:41,390 --> 00:16:43,460
won't stay in their bodies for
very long, it will get

379
00:16:43,460 --> 00:16:45,230
excreted out through
their urine.

380
00:16:45,230 --> 00:16:47,960
So they were not thinking about
how quickly they could

381
00:16:47,960 --> 00:16:50,590
run into trouble in the
long sea voyages.

382
00:16:50,590 --> 00:16:54,360
And I don't know how many of you
had a unit on explorers in

383
00:16:54,360 --> 00:16:55,610
elementary school --

384
00:16:55,610 --> 00:16:58,500
I did in fifth grade, and one
that always sticks in my head

385
00:16:58,500 --> 00:17:02,245
is Magellan's trip around the
world, who led the first fleet

386
00:17:02,245 --> 00:17:03,790
of ships around the globe.

387
00:17:03,790 --> 00:17:07,310
What they did not mention to us
in fifth grade was that 90%

388
00:17:07,310 --> 00:17:10,020
of his men died on
that journey.

389
00:17:10,020 --> 00:17:14,030
And I understand we were young
kids, I didn't want to know

390
00:17:14,030 --> 00:17:16,510
that at the time, but it's
interesting and it's really

391
00:17:16,510 --> 00:17:18,460
important, and the reason
for many of

392
00:17:18,460 --> 00:17:19,470
these deaths was scurvy.

393
00:17:19,470 --> 00:17:22,350
And it's totally preventable.

394
00:17:22,350 --> 00:17:25,420
And, in fact, the cure for
scurvy, which is as simple as

395
00:17:25,420 --> 00:17:29,970
taking vitamin C in any form,
was known for -- since the

396
00:17:29,970 --> 00:17:32,930
fifth century people started
figuring this out, but the

397
00:17:32,930 --> 00:17:36,420
problem was there was so much
false information as well that

398
00:17:36,420 --> 00:17:39,530
it was not a general practice
on ships to be treating men

399
00:17:39,530 --> 00:17:42,000
that were suffering with vitamin
C or using it as any

400
00:17:42,000 --> 00:17:43,790
kind of preventative measure.

401
00:17:43,790 --> 00:17:45,940
The other somewhat interesting
thing I want to say about

402
00:17:45,940 --> 00:17:49,040
vitamin C is that it was part
of the first ever published

403
00:17:49,040 --> 00:17:50,520
clinical study.

404
00:17:50,520 --> 00:17:53,270
And this was a controlled
clinical study that was done

405
00:17:53,270 --> 00:17:56,790
in the 1700's, the first one
that's ever been reported, and

406
00:17:56,790 --> 00:17:59,700
not surprisingly it was done on
a ship and it was done by

407
00:17:59,700 --> 00:18:02,520
James Lind who was a Scottish
naval surgeon.

408
00:18:02,520 --> 00:18:05,260
And basically, he took 12 of
his men, so this was not a

409
00:18:05,260 --> 00:18:08,800
very large clinical study like
they do today, but he took 12

410
00:18:08,800 --> 00:18:11,680
men that were suffering from
scurvy, and he gave them a

411
00:18:11,680 --> 00:18:15,300
diet mostly of just carbohydrate
mush, because

412
00:18:15,300 --> 00:18:17,860
when you have scurvy, one of
the first signs is bleeding

413
00:18:17,860 --> 00:18:19,540
gums and teeth falling
out, they couldn't

414
00:18:19,540 --> 00:18:20,580
really eat too much.

415
00:18:20,580 --> 00:18:22,570
But he supplemented
their diet.

416
00:18:22,570 --> 00:18:24,550
He put them in pairs of two and

417
00:18:24,550 --> 00:18:26,980
supplemented with 1 of 6 things.

418
00:18:26,980 --> 00:18:29,900
So two of them got a
pint of cider a day

419
00:18:29,900 --> 00:18:31,580
to see if that helped.

420
00:18:31,580 --> 00:18:35,200
Two of them got half a pint of
seawater -- maybe not the best

421
00:18:35,200 --> 00:18:36,330
group to be in.

422
00:18:36,330 --> 00:18:38,490
Even worse group to be in is
two of them got diluted

423
00:18:38,490 --> 00:18:40,760
sulfuric acid.

424
00:18:40,760 --> 00:18:43,480
Tuned out that didn't
help so well.

425
00:18:43,480 --> 00:18:47,630
Other things where some got
spices, not so bad.

426
00:18:47,630 --> 00:18:50,250
And then two of them actually
got citrus fruit.

427
00:18:50,250 --> 00:18:53,760
So no big surprise ending to
this clinical study, the

428
00:18:53,760 --> 00:18:57,580
people with citrus fruit were
completely cured and back to

429
00:18:57,580 --> 00:19:00,320
duty within a week, and I'm not
sure exactly what happened

430
00:19:00,320 --> 00:19:02,600
to everyone else, but
let's hope they got

431
00:19:02,600 --> 00:19:05,170
switched over as well.

432
00:19:05,170 --> 00:19:07,730
But it's just neat to think
about even back then, people

433
00:19:07,730 --> 00:19:10,600
were doing these controlled
scientific studies, this was

434
00:19:10,600 --> 00:19:12,190
one of the first cases.

435
00:19:12,190 --> 00:19:16,350
Unfortunately, it was another
40 years between this study

436
00:19:16,350 --> 00:19:19,180
being published and the
British Navy requiring

437
00:19:19,180 --> 00:19:20,150
supplements of citric acid.

438
00:19:20,150 --> 00:19:24,320
So, really, we've come a long
way in terms of disseminating

439
00:19:24,320 --> 00:19:26,740
scientific knowledge to the
community, and that's a really

440
00:19:26,740 --> 00:19:29,510
important part of being
scientists -- not just making

441
00:19:29,510 --> 00:19:32,680
these discoveries, but also
passing along, for example, to

442
00:19:32,680 --> 00:19:36,060
these ships full of people
that need to know it.

443
00:19:36,060 --> 00:19:38,850
So, in terms of scurvy, we
don't see too much of it

444
00:19:38,850 --> 00:19:42,230
today, but who should
be concerned about

445
00:19:42,230 --> 00:19:43,600
suffering from scurvy?

446
00:19:43,600 --> 00:19:46,700
Do we have to worry about our
cats or dogs at home, are they

447
00:19:46,700 --> 00:19:49,580
getting enough of their
vegetables and vitamin C?

448
00:19:49,580 --> 00:19:51,270
It turns out we don't
have to worry.

449
00:19:51,270 --> 00:19:54,080
Primates are who should
be concerned.

450
00:19:54,080 --> 00:19:55,820
So we need to be concerned,
other

451
00:19:55,820 --> 00:19:57,740
primates need to be concerned.

452
00:19:57,740 --> 00:20:01,120
It turns out that most other
mammals actually biosynthesize

453
00:20:01,120 --> 00:20:03,870
vitamin C, so we don't have
to worry about most

454
00:20:03,870 --> 00:20:07,040
of our pets at home.

455
00:20:07,040 --> 00:20:10,040
Unless you have a guinea pig
and they don't, in fact,

456
00:20:10,040 --> 00:20:13,870
biosynthesize vitamin C, so I
think they supplement most

457
00:20:13,870 --> 00:20:16,240
guinea pig pellets with vitamin
C, but maybe keep an

458
00:20:16,240 --> 00:20:18,470
eye on your guinea pig.

459
00:20:18,470 --> 00:20:21,320
We primates and guinea pigs are
the only types of mammals

460
00:20:21,320 --> 00:20:24,430
that don't actually
biosynthesize their vitamin C.

461
00:20:24,430 --> 00:20:27,660
So again, vitamin C is a
cofactor, that means it needs

462
00:20:27,660 --> 00:20:31,530
to bind to an enzyme, it means
that the shape of vitamin C

463
00:20:31,530 --> 00:20:34,200
and the hybridization are going
to be really important.

464
00:20:34,200 --> 00:20:37,540
So let's take a look and talk
about some of these carbon

465
00:20:37,540 --> 00:20:38,780
atoms here.

466
00:20:38,780 --> 00:20:41,230
And you can look at your
structure of vitamin C in your

467
00:20:41,230 --> 00:20:44,010
class notes while you're doing
this, and first I want you to

468
00:20:44,010 --> 00:20:48,940
tell me what the hybridization
is of that carbon a in the

469
00:20:48,940 --> 00:20:59,780
vitamin C molecule.

470
00:20:59,780 --> 00:21:14,800
And let's take 10 more
seconds on that.

471
00:21:14,800 --> 00:21:16,620
OK, 78%.

472
00:21:16,620 --> 00:21:18,730
We'll do another question
like this in a minute.

473
00:21:18,730 --> 00:21:21,950
So if we can switch back
to the notes we'll

474
00:21:21,950 --> 00:21:23,520
take a look at that.

475
00:21:23,520 --> 00:21:25,590
I think we can get better, I
think we can get to the 90's

476
00:21:25,590 --> 00:21:28,260
with these hybridization, we
just need to follow the rules.

477
00:21:28,260 --> 00:21:30,910
So if we're thinking about
vitamin C and we're talking

478
00:21:30,910 --> 00:21:34,860
about carbon a, how many things
is carbon a bonded to?

479
00:21:34,860 --> 00:21:36,400
STUDENT: [INAUDIBLE]

480
00:21:36,400 --> 00:21:36,940
PROFESSOR: four things.

481
00:21:36,940 --> 00:21:39,210
We have two hydrogen atoms,
an oxygen, and

482
00:21:39,210 --> 00:21:40,480
then another carbon.

483
00:21:40,480 --> 00:21:44,460
So that means we need, if it's
bonded to four things, we need

484
00:21:44,460 --> 00:21:47,680
four different hybrid orbitals,
so it needs to be s

485
00:21:47,680 --> 00:21:51,150
p 3 hybridized.

486
00:21:51,150 --> 00:21:54,320
All right, let's try this again
but just shouting out,

487
00:21:54,320 --> 00:21:57,990
what is the hybridization
of carbon b?

488
00:21:57,990 --> 00:21:59,230
Good.

489
00:21:59,230 --> 00:22:01,910
OK, I'm going to say that was
about 90% of you I heard,

490
00:22:01,910 --> 00:22:03,240
which is excellent.

491
00:22:03,240 --> 00:22:04,370
S p 3.

492
00:22:04,370 --> 00:22:06,890
What about carbon c here?

493
00:22:06,890 --> 00:22:11,840
Yup, s p 3 again.

494
00:22:11,840 --> 00:22:14,310
Bonded to four things
it's s p 3.

495
00:22:14,310 --> 00:22:17,300
What about carbon d?

496
00:22:17,300 --> 00:22:20,510
S p 2, great.

497
00:22:20,510 --> 00:22:21,450
Carbon e?

498
00:22:21,450 --> 00:22:24,710
STUDENT: S p 2.

499
00:22:24,710 --> 00:22:26,610
PROFESSOR: All right, and this
last one, the last 10% of you

500
00:22:26,610 --> 00:22:27,380
can join in.

501
00:22:27,380 --> 00:22:28,970
Carbon f?

502
00:22:28,970 --> 00:22:31,200
Great, s p 2.

503
00:22:31,200 --> 00:22:36,100
All right, so we can also think
about shape once we know

504
00:22:36,100 --> 00:22:38,800
hybridization and how
many atoms a carbon

505
00:22:38,800 --> 00:22:39,990
atom is bonded to.

506
00:22:39,990 --> 00:22:43,150
What would we say that the
shape is of these s p 3

507
00:22:43,150 --> 00:22:47,930
orbitals -- or the shape
of the carbon atom.

508
00:22:47,930 --> 00:22:52,160
Yeah, it's tetrahedral.

509
00:22:52,160 --> 00:22:57,610
So this is going to
be tetrahedral.

510
00:22:57,610 --> 00:23:00,950
And what about carbon
d, e, and f?

511
00:23:00,950 --> 00:23:04,750
What is the geometry of
carbon d, e, and f?

512
00:23:04,750 --> 00:23:06,160
Good, trigonal planar.

513
00:23:06,160 --> 00:23:14,750
All right.

514
00:23:14,750 --> 00:23:17,590
So let's actually take this
one step further from just

515
00:23:17,590 --> 00:23:19,810
talking about the hybridization
of the

516
00:23:19,810 --> 00:23:20,700
individual atom.

517
00:23:20,700 --> 00:23:22,950
Let's talk about a couple
of these bonds.

518
00:23:22,950 --> 00:23:24,700
I won't go through
all of them.

519
00:23:24,700 --> 00:23:27,040
I think you can get the idea
with just a few, but you can

520
00:23:27,040 --> 00:23:30,150
go back and try all
of them later.

521
00:23:30,150 --> 00:23:34,950
So let's start with thinking
about carbon b hydrogen bond.

522
00:23:34,950 --> 00:23:38,330
Is this going to be a
sigma or a pi bond?

523
00:23:38,330 --> 00:23:38,650
Sigma.

524
00:23:38,650 --> 00:23:42,510
We know it's sigma, because any
time we have a single bond

525
00:23:42,510 --> 00:23:45,040
it's a sigma bond.

526
00:23:45,040 --> 00:23:48,220
So carbon b, we just said,
is carbon, it's

527
00:23:48,220 --> 00:23:51,590
going to be 2 s p 3.

528
00:23:51,590 --> 00:23:54,240
And then hydrogen, what's the
atomic orbital we're talking

529
00:23:54,240 --> 00:23:55,770
about here?

530
00:23:55,770 --> 00:23:57,700
1 s.

531
00:23:57,700 --> 00:23:58,420
All right, great.

532
00:23:58,420 --> 00:24:00,870
So let's take a look at another
one, let's look again

533
00:24:00,870 --> 00:24:04,340
at carbon b, but now let's talk
about it bonding to its

534
00:24:04,340 --> 00:24:06,200
oxygen there.

535
00:24:06,200 --> 00:24:08,730
So again, are we going
to be talking about a

536
00:24:08,730 --> 00:24:11,710
sigma or a pi bond?

537
00:24:11,710 --> 00:24:16,110
A sigma bond, because again,
it's a single bond here.

538
00:24:16,110 --> 00:24:21,880
So what we'll say again is
carbon 2 s p 3, and let's take

539
00:24:21,880 --> 00:24:24,930
a look at this oxygen
that it's bound to.

540
00:24:24,930 --> 00:24:28,530
Is this oxygen -- what is the
hybridization of this oxygen

541
00:24:28,530 --> 00:24:30,980
right here?

542
00:24:30,980 --> 00:24:32,850
What is it?

543
00:24:32,850 --> 00:24:35,010
OK, good, it's s p 3.

544
00:24:35,010 --> 00:24:38,160
It's bound to two atoms, plus it
has two lone pairs, that's

545
00:24:38,160 --> 00:24:39,980
a total of four things.

546
00:24:39,980 --> 00:24:42,950
So it needs to have three
different hybrid orbitals, so

547
00:24:42,950 --> 00:24:51,150
we'll say it's oxygen 2 s p 3.

548
00:24:51,150 --> 00:24:53,980
So let's skip to a different
carbon now, let's talk about

549
00:24:53,980 --> 00:24:58,550
carbon d, specifically the
carbon d oxygen bond.

550
00:24:58,550 --> 00:25:01,030
So let's do a clicker question
for this one.

551
00:25:01,030 --> 00:25:04,510
Let's get into the 90's, if you
don't mind, this would be

552
00:25:04,510 --> 00:25:06,320
very good to do.

553
00:25:06,320 --> 00:25:08,120
It'll make me feel better
about you finishing your

554
00:25:08,120 --> 00:25:10,810
problem-sets tonight.

555
00:25:10,810 --> 00:25:15,790
So if you talk about the
symmetry and the hybrid or

556
00:25:15,790 --> 00:25:18,660
atomic orbitals that contribute,
we're talking

557
00:25:18,660 --> 00:25:20,390
about the c d oxygen bond.

558
00:25:20,390 --> 00:25:22,310
So go ahead and look at
your notes and see

559
00:25:22,310 --> 00:25:24,370
what that bond is.

560
00:25:24,370 --> 00:25:27,950
We already identified the
hybridization of carbon d, so

561
00:25:27,950 --> 00:25:30,260
we really just need to think
about the oxygen here.

562
00:25:30,260 --> 00:26:04,340
All right, let's take
10 more seconds.

563
00:26:04,340 --> 00:26:07,230
OK, I'll take that, 84%.

564
00:26:07,230 --> 00:26:10,010
That's not bad.

565
00:26:10,010 --> 00:26:12,790
So again, we're looking
at a sigma bond here.

566
00:26:12,790 --> 00:26:15,170
It looks like the one people
got it confused with was

567
00:26:15,170 --> 00:26:18,660
talking about oxygen
s p 2 versus s p 3.

568
00:26:18,660 --> 00:26:20,710
Remember, you just need to look
at what it is actually

569
00:26:20,710 --> 00:26:24,260
bound to, so for carbon d, the
oxygen's bound to two atoms

570
00:26:24,260 --> 00:26:27,890
plus two lone pairs, so it's
going to be s p 3 hybridized.

571
00:26:27,890 --> 00:26:32,660
So we'll call this a sigma bond
where we have carbon 2 s

572
00:26:32,660 --> 00:26:37,960
p, now it's s p 2, and
oxygen 2 s p 3.

573
00:26:37,960 --> 00:26:41,300
All right, let's take a look
at just one more here.

574
00:26:41,300 --> 00:26:45,430
So, let's look at the carbon
d bond with carbon e.

575
00:26:45,430 --> 00:26:48,750
So if we can switch back to the
class notes just to see

576
00:26:48,750 --> 00:26:51,780
that, though you guys can see
it on your notes as well.

577
00:26:51,780 --> 00:26:54,300
So in terms of that, we're
talking about a double bond

578
00:26:54,300 --> 00:26:57,650
now, so we know that we have to
have one sigma bond and one

579
00:26:57,650 --> 00:27:01,090
pi bond to completely describe
our double bond.

580
00:27:01,090 --> 00:27:03,220
So for the sigma bond, again,
it's going to be

581
00:27:03,220 --> 00:27:07,710
carbon 2 s p 2.

582
00:27:07,710 --> 00:27:09,780
And now we're talking about
the other carbon.

583
00:27:09,780 --> 00:27:13,660
What is the hybridization
of the other carbon?

584
00:27:13,660 --> 00:27:14,660
Yup, s p 2.

585
00:27:14,660 --> 00:27:17,040
So carbon 2 s p 2.

586
00:27:17,040 --> 00:27:19,420
All right, but we're
not done there.

587
00:27:19,420 --> 00:27:22,250
We also need to talk
about the pi bond.

588
00:27:22,250 --> 00:27:26,730
So for the pi bond, we'll talk
about carbon 2 p y, and then

589
00:27:26,730 --> 00:27:29,110
the second carbon 2 p y.

590
00:27:29,110 --> 00:27:33,970
All right, so I filled in a few
more in your notes, so you

591
00:27:33,970 --> 00:27:36,340
can maybe cover those up and
make sure that you get all of

592
00:27:36,340 --> 00:27:40,330
those correct is a good self
test before you finish off any

593
00:27:40,330 --> 00:27:41,490
in your problem-set.

594
00:27:41,490 --> 00:27:43,920
Does anyone have any questions
about figuring out

595
00:27:43,920 --> 00:27:44,580
hybridization?

596
00:27:44,580 --> 00:27:44,810
Yes?

597
00:27:44,810 --> 00:27:48,750
STUDENT: [INAUDIBLE]

598
00:27:48,750 --> 00:27:52,450
PROFESSOR: I'm sorry,
what is that?

599
00:27:52,450 --> 00:27:54,200
In this bond here?

600
00:27:54,200 --> 00:27:55,310
Oh, OK, that's a
good question.

601
00:27:55,310 --> 00:27:57,740
So the question was why is there
not hybridization in

602
00:27:57,740 --> 00:27:59,290
these p orbitals here.

603
00:27:59,290 --> 00:28:03,250
So in order to form a double
bond, we need to have a pi

604
00:28:03,250 --> 00:28:05,060
bond forms, and a pi
bond forms from two

605
00:28:05,060 --> 00:28:06,720
unhybridized p orbitals.

606
00:28:06,720 --> 00:28:09,640
And if you can kind of picture
those p orbitals, if our

607
00:28:09,640 --> 00:28:12,170
molecules are this way and
they're coming up here, we

608
00:28:12,170 --> 00:28:14,530
need to have electron density
above the bond

609
00:28:14,530 --> 00:28:15,710
and below the bond.

610
00:28:15,710 --> 00:28:18,000
So if they're hybrid, then
they're going to be spread out

611
00:28:18,000 --> 00:28:20,120
into that tetrahedral
geometry.

612
00:28:20,120 --> 00:28:23,130
We want to have them parallel to
each other and they need to

613
00:28:23,130 --> 00:28:25,420
be the p bonds, they need
to be the p orbitals.

614
00:28:25,420 --> 00:28:28,440
Does that makes sense?

615
00:28:28,440 --> 00:28:33,330
So any time we have a double
bond, the pi part of the bond

616
00:28:33,330 --> 00:28:34,100
is going to be p orbitals.

617
00:28:34,100 --> 00:28:34,180
Yes?

618
00:28:34,180 --> 00:28:34,740
STUDENT: [INAUDIBLE]

619
00:28:34,740 --> 00:28:38,360
PROFESSOR: No, absolutely not.

620
00:28:38,360 --> 00:28:42,490
It would be absolutely correct
to put 2 p x and 2 p x here,

621
00:28:42,490 --> 00:28:45,130
you just can't put z, because
that's the one that's going to

622
00:28:45,130 --> 00:28:46,660
be involved in the sigma bond.

623
00:28:46,660 --> 00:28:49,740
And the other important thing
is if you do put x for one,

624
00:28:49,740 --> 00:28:52,010
you have to make sure you put
x in the other, because they

625
00:28:52,010 --> 00:28:54,470
do need to be able to interact
with each other.

626
00:28:54,470 --> 00:28:57,490
You can't have one x and one y,
but sure, you can have both

627
00:28:57,490 --> 00:29:02,160
x or both y.

628
00:29:02,160 --> 00:29:05,240
OK, so let's shift gears a
little bit and start talking

629
00:29:05,240 --> 00:29:11,120
about bonding in terms of
chemical reactions.

630
00:29:11,120 --> 00:29:13,820
So we're going to start today
with talking about bond

631
00:29:13,820 --> 00:29:19,760
energies, and also something
called bond enthalpies.

632
00:29:19,760 --> 00:29:22,310
And the first point is just to
bring us back to something

633
00:29:22,310 --> 00:29:23,490
we're very familiar with.

634
00:29:23,490 --> 00:29:26,580
When we talked about covalent
bonding, a concept that we

635
00:29:26,580 --> 00:29:29,930
have been discussing is bond
dissociation energy.

636
00:29:29,930 --> 00:29:33,210
That's just the energy that's
required to put into a

637
00:29:33,210 --> 00:29:35,590
molecule in order to
break that bond.

638
00:29:35,590 --> 00:29:38,570
This is something that we saw
when we were talking just at

639
00:29:38,570 --> 00:29:41,410
the very beginning of our
unit on covalent bonds.

640
00:29:41,410 --> 00:29:45,450
That energy difference is the
energy difference between when

641
00:29:45,450 --> 00:29:49,180
we have the c h 4, if we're
talking about methane, versus

642
00:29:49,180 --> 00:29:52,460
one of those hydrogen bonds
breaking, one of those c h

643
00:29:52,460 --> 00:29:53,800
bonds breaking.

644
00:29:53,800 --> 00:29:58,080
So we've talked in the past
about bond energy, but what I

645
00:29:58,080 --> 00:30:01,560
want to introduce to you today
is a very related concept,

646
00:30:01,560 --> 00:30:03,380
which is called bond enthalpy.

647
00:30:03,380 --> 00:30:08,400
So that's delta h here is what
we call bond enthalpy.

648
00:30:08,400 --> 00:30:10,870
So, this is talking about
instead of the change of

649
00:30:10,870 --> 00:30:14,380
energy accompanied with a bond
breaking, we're talking about

650
00:30:14,380 --> 00:30:17,350
a change in heat accompanied
with a bond breaking.

651
00:30:17,350 --> 00:30:20,920
So whether when that bond breaks
it requires heat, or

652
00:30:20,920 --> 00:30:24,310
whether it gives off heat when
you break that bond or talking

653
00:30:24,310 --> 00:30:25,060
about a reaction.

654
00:30:25,060 --> 00:30:26,250
That's what we're talking
about when we're

655
00:30:26,250 --> 00:30:28,770
talking about enthalpy.

656
00:30:28,770 --> 00:30:31,690
It turns out that enthalpy is,
in fact, very related to

657
00:30:31,690 --> 00:30:35,350
energy, and we can relate it
with this equation here that

658
00:30:35,350 --> 00:30:39,420
bond enthalpy is equal to bond
energy plus the change in

659
00:30:39,420 --> 00:30:41,350
pressure times volume.

660
00:30:41,350 --> 00:30:44,120
So we could, in fact, go back
and forth between bond

661
00:30:44,120 --> 00:30:47,670
energies and bond enthalpies,
but the reality is if we're

662
00:30:47,670 --> 00:30:50,970
talking about gases, which we
are in many cases, then what

663
00:30:50,970 --> 00:30:54,100
we find is the difference
between bond enthalpy and bond

664
00:30:54,100 --> 00:30:57,000
energy is only 1% to 2%.

665
00:30:57,000 --> 00:30:58,770
So it's not very significant.

666
00:30:58,770 --> 00:31:02,390
And, in fact, if we're talking
about solids or liquids, now

667
00:31:02,390 --> 00:31:05,460
we can say that the difference
between bond energy and bond

668
00:31:05,460 --> 00:31:07,910
enthalpy is going to
be negligible.

669
00:31:07,910 --> 00:31:11,410
So, for the rest of this class
today, we're going to stop

670
00:31:11,410 --> 00:31:13,880
talking about bond energy, which
I did just for a moment,

671
00:31:13,880 --> 00:31:16,880
to orient you back to a
discussion that was familiar,

672
00:31:16,880 --> 00:31:19,770
we're going to switch our
discussion to bond enthalpies.

673
00:31:19,770 --> 00:31:22,780
One reason that we like to
talk about enthalpies is

674
00:31:22,780 --> 00:31:26,040
unlike energy, which can be a
little bit more tricky, bond

675
00:31:26,040 --> 00:31:27,970
enthalpies are easy
to measure.

676
00:31:27,970 --> 00:31:31,330
It's easy to measure how much
heat a reaction gives off or

677
00:31:31,330 --> 00:31:35,790
how much heat a reaction
takes in.

678
00:31:35,790 --> 00:31:38,550
So we can also talk about
something, which is called the

679
00:31:38,550 --> 00:31:42,020
standard bond enthalpy, so any
time you see this symbol here,

680
00:31:42,020 --> 00:31:45,110
which looks like a knot, so it
looks like a delta h knot,

681
00:31:45,110 --> 00:31:48,110
that refers to the standard
bond enthalpy.

682
00:31:48,110 --> 00:31:50,680
Any time we we're talking about
a standard, whether it's

683
00:31:50,680 --> 00:31:53,900
enthalpy or, as we'll see in
the next lecture, standard

684
00:31:53,900 --> 00:31:57,680
entropy or a standard free
energy, we're just saying that

685
00:31:57,680 --> 00:32:00,450
the molecules that we're talking
about are in their

686
00:32:00,450 --> 00:32:03,440
standard states, which means
they're in their pure form.

687
00:32:03,440 --> 00:32:05,850
If they're a gas it means
they're at one bar.

688
00:32:05,850 --> 00:32:07,740
Usually this is referring
to room

689
00:32:07,740 --> 00:32:11,070
temperature, so 298 kelvin.

690
00:32:11,070 --> 00:32:14,570
It's often that when you look
up tables of different bond

691
00:32:14,570 --> 00:32:17,215
enthalpies, you'll see them in
their standard state and it

692
00:32:17,215 --> 00:32:18,710
will be at room temperature.

693
00:32:18,710 --> 00:32:21,830
So if we talk about standard
bond enthalpy, let's talk

694
00:32:21,830 --> 00:32:24,450
about what this is for these
c h bonds, which

695
00:32:24,450 --> 00:32:26,280
we just saw in methane.

696
00:32:26,280 --> 00:32:29,820
So if we're going from c h 4 to
breaking one of these c h

697
00:32:29,820 --> 00:32:32,990
bonds, what we see is that
the bond enthalpy is 438

698
00:32:32,990 --> 00:32:33,640
kilojoules per mole.

699
00:32:33,640 --> 00:32:37,650
The fact that it's positive
tells us that we need to put

700
00:32:37,650 --> 00:32:40,090
in that much heat into
the system in order

701
00:32:40,090 --> 00:32:42,240
to break that bond.

702
00:32:42,240 --> 00:32:45,060
So we now know the enthalpy of
a c h bond, but, of course,

703
00:32:45,060 --> 00:32:47,520
methane is not the only
kind of c h bond

704
00:32:47,520 --> 00:32:48,850
that you can envision.

705
00:32:48,850 --> 00:32:52,180
We could talk about the c h
bond, for example, in ethane

706
00:32:52,180 --> 00:32:56,650
or trifluoromethane or trichloro
or tribromomethane,

707
00:32:56,650 --> 00:32:59,570
and what you'll find is that
the amount of enthalpy that

708
00:32:59,570 --> 00:33:03,140
that reaction is associated with
depends on the exact type

709
00:33:03,140 --> 00:33:06,470
of c h bond that you have. So,
for example, we can see that

710
00:33:06,470 --> 00:33:09,060
we have slightly different,
not vastly different, but

711
00:33:09,060 --> 00:33:12,690
slightly different changes in
enthalpy depending on which

712
00:33:12,690 --> 00:33:17,090
kind of c h bond that
were breaking.

713
00:33:17,090 --> 00:33:19,570
And what I want to point out
also is that all of these

714
00:33:19,570 --> 00:33:21,690
delta h's, all of these
standard bond

715
00:33:21,690 --> 00:33:23,580
enthalpies are positive.

716
00:33:23,580 --> 00:33:27,420
Any time we have a positive
delta h, we call this an

717
00:33:27,420 --> 00:33:29,320
endothermic reaction.

718
00:33:29,320 --> 00:33:32,080
And again, endothermic
just means that the

719
00:33:32,080 --> 00:33:34,380
reaction takes in energy.

720
00:33:34,380 --> 00:33:37,220
It's very similar to what when
we're talking about energy

721
00:33:37,220 --> 00:33:40,125
whether something's taken in
or released, whether it's

722
00:33:40,125 --> 00:33:41,060
positive or negative.

723
00:33:41,060 --> 00:33:44,510
If you have positive delta h,
it's endothermic, it takes in

724
00:33:44,510 --> 00:33:48,040
heat in order for the
reaction to go.

725
00:33:48,040 --> 00:33:50,830
So we can think about instead of
talking about all of these

726
00:33:50,830 --> 00:33:54,840
individual c h bonds, instead
we can talk about what the

727
00:33:54,840 --> 00:33:57,090
average value would be
for all c h bonds.

728
00:33:57,090 --> 00:34:00,610
So we can say that the average
of any c h bond is 412

729
00:34:00,610 --> 00:34:02,010
kilojoules per mole.

730
00:34:02,010 --> 00:34:04,360
So you can imagine if you're
looking these things up in

731
00:34:04,360 --> 00:34:06,910
terms of a reference table or
maybe in the appendix of your

732
00:34:06,910 --> 00:34:10,140
textbook, it would be an
impossibly huge number of

733
00:34:10,140 --> 00:34:13,630
pages to write every single
different kinds of c h bond.

734
00:34:13,630 --> 00:34:16,650
So that's why instead they talk
about the average bond

735
00:34:16,650 --> 00:34:17,680
enthalpies.

736
00:34:17,680 --> 00:34:21,370
So for c h, again, that's 412,
and all of the enthalpies we

737
00:34:21,370 --> 00:34:24,360
just saw fall within
about 8% of that.

738
00:34:24,360 --> 00:34:27,710
And in your book you can look
up any type of bond that's

739
00:34:27,710 --> 00:34:28,680
listed here.

740
00:34:28,680 --> 00:34:30,840
So we saw c h is 412.

741
00:34:30,840 --> 00:34:34,110
You can look up a c c bond, you
can look up a c c double

742
00:34:34,110 --> 00:34:36,610
bond, a c c triple
bond, and so on.

743
00:34:36,610 --> 00:34:39,270
And you'll note that what
these are are mean bond

744
00:34:39,270 --> 00:34:41,990
enthalpies, so they're the
average of all different types

745
00:34:41,990 --> 00:34:47,300
of c h bonds or c c bonds
that you can imagine.

746
00:34:47,300 --> 00:34:50,360
So, you might be asking what's
so important about being able

747
00:34:50,360 --> 00:34:52,710
to look up and think about
these different bond

748
00:34:52,710 --> 00:34:53,670
enthalpies.

749
00:34:53,670 --> 00:34:55,890
And the reason that it's
important is because if you're

750
00:34:55,890 --> 00:34:58,660
looking at a reaction, no matter
how complicated that

751
00:34:58,660 --> 00:35:02,540
reaction is, you can actually
figure out what the enthalpy

752
00:35:02,540 --> 00:35:06,210
of the entire reaction is by
adding up all the individual

753
00:35:06,210 --> 00:35:09,720
mean bond enthalpies of the
products, and all the

754
00:35:09,720 --> 00:35:12,760
individual mean bond enthalpies
of their reactants

755
00:35:12,760 --> 00:35:15,480
and thinking about the
difference between those two.

756
00:35:15,480 --> 00:35:18,240
So we'll do that in just a
second, and the reaction that

757
00:35:18,240 --> 00:35:21,330
we'll do it with is the
oxidation of glucose here.

758
00:35:21,330 --> 00:35:26,733
So, c 6 h 12 o 6, one mole of
glucose plus six moles of

759
00:35:26,733 --> 00:35:29,610
oxygen, gives us six moles
of carbon dioxide and

760
00:35:29,610 --> 00:35:31,320
six moles of water.

761
00:35:31,320 --> 00:35:34,310
So what we can find out, and
hopefully what we will match

762
00:35:34,310 --> 00:35:37,700
up when we look at using the
different bond enthalpies, is

763
00:35:37,700 --> 00:35:41,250
that the enthalpy of this entire
reaction is negative

764
00:35:41,250 --> 00:35:44,220
2816 kilojoules per mole.

765
00:35:44,220 --> 00:35:47,200
So in this case we're saying
that delta h is negative.

766
00:35:47,200 --> 00:35:48,400
Does anyone know what
it's called

767
00:35:48,400 --> 00:35:51,030
when delta h is negative?

768
00:35:51,030 --> 00:35:52,280
Everyone knows, great.

769
00:35:52,280 --> 00:35:52,960
So it's exothermic.

770
00:35:52,960 --> 00:35:56,500
This is an exothermic reaction,
the reaction

771
00:35:56,500 --> 00:35:59,870
releases heat.

772
00:35:59,870 --> 00:36:02,420
So I just want to mention before
we go on, if you look

773
00:36:02,420 --> 00:36:06,060
at almost any freshman chemistry
textbook, what

774
00:36:06,060 --> 00:36:09,910
you'll find is this oxidation of
glucose reaction is used a

775
00:36:09,910 --> 00:36:12,820
lot in talking about
thermochemistry.

776
00:36:12,820 --> 00:36:14,920
And one reason it's talked about
is because it's very

777
00:36:14,920 --> 00:36:17,070
convenient to talk about
something where we start with

778
00:36:17,070 --> 00:36:21,120
one mole of glucose and end up
with 12 moles of products.

779
00:36:21,120 --> 00:36:23,290
That's going to be helpful what
we're doing a practice

780
00:36:23,290 --> 00:36:25,740
problem to see exactly how you
deal with it when there's

781
00:36:25,740 --> 00:36:27,330
different numbers of moles.

782
00:36:27,330 --> 00:36:29,570
But the other reason you always
see this reaction is

783
00:36:29,570 --> 00:36:32,030
because it's an incredibly
important reaction.

784
00:36:32,030 --> 00:36:34,840
The oxidation of glucose is
going on all the time in our

785
00:36:34,840 --> 00:36:39,620
body, this is our main source
of energy for all animals.

786
00:36:39,620 --> 00:36:42,600
So let's think a little bit
about why this reaction is so

787
00:36:42,600 --> 00:36:44,170
important and so prevalent.

788
00:36:44,170 --> 00:36:46,950
It turns out that if we're
talking about plants, plants

789
00:36:46,950 --> 00:36:48,620
do the reverse reaction.

790
00:36:48,620 --> 00:36:52,130
So plants take carbon dioxide
and water and they turn it

791
00:36:52,130 --> 00:36:55,720
into glucose or energy for us,
energy stored in the bonds of

792
00:36:55,720 --> 00:36:58,850
glucose plus oxygen.

793
00:36:58,850 --> 00:37:01,220
So if we do the reverse
reaction, this is actually

794
00:37:01,220 --> 00:37:02,960
going to require energy.

795
00:37:02,960 --> 00:37:06,080
Where do plants get
this energy?

796
00:37:06,080 --> 00:37:07,520
Yeah, this is just
photosynthesis here.

797
00:37:07,520 --> 00:37:10,430
This is the photosynthesis
where plants are turning

798
00:37:10,430 --> 00:37:15,120
carbon dioxide and water into
sugar and into oxygen.

799
00:37:15,120 --> 00:37:17,990
So what happens when we eat
the plants or when we eat

800
00:37:17,990 --> 00:37:21,080
animals that have eaten the
plants is that we perform the

801
00:37:21,080 --> 00:37:23,990
reverse reaction now, which is
what I just showed you, the

802
00:37:23,990 --> 00:37:24,660
oxidation of glucose.

803
00:37:24,660 --> 00:37:29,230
And even though it's not the
products of the reaction that

804
00:37:29,230 --> 00:37:32,070
are particularly valuable to us,
we just breathe out the c

805
00:37:32,070 --> 00:37:36,040
o 2, and actually we'd rather
have less of that than more in

806
00:37:36,040 --> 00:37:40,640
our environment, but what's
important here is instead the

807
00:37:40,640 --> 00:37:43,990
energy or the enthalpy that's
given often in this reaction.

808
00:37:43,990 --> 00:37:47,240
So as I said, this reaction
has a negative enthalpy of

809
00:37:47,240 --> 00:37:49,920
2816 kilojoules per mole.

810
00:37:49,920 --> 00:37:52,560
That's a lot of enthalpy
and a lot of energy.

811
00:37:52,560 --> 00:37:56,170
So we actually end up using that
energy to fuel most of

812
00:37:56,170 --> 00:37:57,610
what is going on
in our bodies.

813
00:37:57,610 --> 00:38:01,400
So instead of storing it as
sugar, once we oxidize the

814
00:38:01,400 --> 00:38:05,240
sugar, now we just store it as
ATP, and as you know, ATP is

815
00:38:05,240 --> 00:38:07,480
the currency of energy
in the cells.

816
00:38:07,480 --> 00:38:10,350
So this is why you see this
reaction again and again and

817
00:38:10,350 --> 00:38:12,630
again in just about any
chemistry textbook that you

818
00:38:12,630 --> 00:38:15,040
open up as sort of a
general reaction.

819
00:38:15,040 --> 00:38:17,920
The reason it's used is it's
just so important and so

820
00:38:17,920 --> 00:38:21,930
prevalent in terms of thinking
about our bodies and how we're

821
00:38:21,930 --> 00:38:24,890
staying alive and
using energy.

822
00:38:24,890 --> 00:38:27,240
All right, so let's go ahead and
use this as an example of

823
00:38:27,240 --> 00:38:30,170
what we just said, which is
using the bond enthalpies of

824
00:38:30,170 --> 00:38:34,750
the products and the reactants
to figure out the enthalpy of

825
00:38:34,750 --> 00:38:36,620
the entire reaction.

826
00:38:36,620 --> 00:38:39,830
So the way that we do this
is we add up all of the

827
00:38:39,830 --> 00:38:43,520
individual mean bond enthalpies
of the reactants,

828
00:38:43,520 --> 00:38:46,940
and we subtract from that all
of the individual bond

829
00:38:46,940 --> 00:38:49,700
enthalpies of the products.

830
00:38:49,700 --> 00:38:51,830
So we can think about what
this will tell us.

831
00:38:51,830 --> 00:38:55,570
If you think about the fact if
the bonds are stronger in the

832
00:38:55,570 --> 00:38:59,350
products than they were in the
reactants, you can go ahead

833
00:38:59,350 --> 00:39:01,430
and click in and tell me if
you think we'll have a

834
00:39:01,430 --> 00:39:04,490
negative or a positive
delta h here.

835
00:39:04,490 --> 00:39:31,090
All right, let's take 10
more seconds on this.

836
00:39:31,090 --> 00:39:38,250
OK, great, so negative is
correct and some people got

837
00:39:38,250 --> 00:39:39,090
totally mixed up.

838
00:39:39,090 --> 00:39:40,940
Didn't just get one thing --
so let's just focus on the

839
00:39:40,940 --> 00:39:42,900
right answer to start with.

840
00:39:42,900 --> 00:39:45,070
The correct answer is that
it's negative, it's an

841
00:39:45,070 --> 00:39:47,400
exothermic reaction.

842
00:39:47,400 --> 00:39:49,000
And actually, lets switch
to our class

843
00:39:49,000 --> 00:39:50,420
notes to explain why.

844
00:39:50,420 --> 00:39:53,040
And also, this was the quiz
question for today, so whether

845
00:39:53,040 --> 00:39:56,000
you got the answer correct or
incorrect, you get full quiz

846
00:39:56,000 --> 00:39:57,990
points if you did,
in fact, answer.

847
00:39:57,990 --> 00:40:00,620
But let's still focus on the
right answer here and see why

848
00:40:00,620 --> 00:40:01,680
it's correct.

849
00:40:01,680 --> 00:40:04,750
So if we're talking about the
bonds being stronger in the

850
00:40:04,750 --> 00:40:09,290
products, that basically means
that we ended up releasing a

851
00:40:09,290 --> 00:40:12,340
lot of heat when we made those
bonds and the products, and we

852
00:40:12,340 --> 00:40:15,000
didn't have to use up too much
of that heat to break all the

853
00:40:15,000 --> 00:40:16,380
bonds and the reactants.

854
00:40:16,380 --> 00:40:18,190
So that's why we say
that delta h

855
00:40:18,190 --> 00:40:19,340
is going to be negative.

856
00:40:19,340 --> 00:40:23,490
You could also just do it not
conceptually, just plugging it

857
00:40:23,490 --> 00:40:25,920
into the equation, but it's
better to kind of understand

858
00:40:25,920 --> 00:40:27,490
exactly why that is.

859
00:40:27,490 --> 00:40:30,960
It's because it takes more
energy -- you gain more energy

860
00:40:30,960 --> 00:40:32,970
forming the products
than you take

861
00:40:32,970 --> 00:40:34,580
breaking up the reactants.

862
00:40:34,580 --> 00:40:37,320
So if we have the opposite case
here, if the bonds are

863
00:40:37,320 --> 00:40:40,430
stronger in the reactants, now
what we're going to find is

864
00:40:40,430 --> 00:40:43,750
that the delta h of the reaction
is positive and what

865
00:40:43,750 --> 00:40:49,590
you're dealing with is an
endothermic reaction.

866
00:40:49,590 --> 00:40:52,200
So let's go ahead and do this
with our example of the

867
00:40:52,200 --> 00:40:54,320
oxidation of glucose.

868
00:40:54,320 --> 00:40:57,210
So, I've just written out the
glucose molecule so you can

869
00:40:57,210 --> 00:41:01,055
see all of its individual bonds
here since we're going

870
00:41:01,055 --> 00:41:04,210
to be using that information.

871
00:41:04,210 --> 00:41:06,610
So let's start by talking
about the bonds that are

872
00:41:06,610 --> 00:41:10,040
broken in terms of thinking
about all of

873
00:41:10,040 --> 00:41:11,420
the reactants here.

874
00:41:11,420 --> 00:41:14,800
So if we're talking about the
sugar molecule itself, what we

875
00:41:14,800 --> 00:41:18,090
have is we have seven
c h bonds.

876
00:41:18,090 --> 00:41:22,400
And if we add up all the o h
bonds, we have five of those.

877
00:41:22,400 --> 00:41:27,790
How many c o single
bonds do we have?

878
00:41:27,790 --> 00:41:29,690
What do people think?

879
00:41:29,690 --> 00:41:32,030
Yeah. five c o single bonds.

880
00:41:32,030 --> 00:41:36,890
What about c c single bonds?
five of those as well.

881
00:41:36,890 --> 00:41:39,610
C o double bonds?

882
00:41:39,610 --> 00:41:41,360
Just one c o double bond.

883
00:41:41,360 --> 00:41:44,070
And then we have our oxygen
molecule to worry about and we

884
00:41:44,070 --> 00:41:47,150
have six o o double bonds.

885
00:41:47,150 --> 00:41:49,810
So if we add up all of the
bonds are broken, and we

886
00:41:49,810 --> 00:41:52,780
subtract from that the bonds
that are formed, those

887
00:41:52,780 --> 00:41:57,650
strengths, the c double bond
o, we have 12 of those.

888
00:41:57,650 --> 00:42:01,200
And how many o h bonds
do we have?

889
00:42:01,200 --> 00:42:02,960
Right, 12 as well.

890
00:42:02,960 --> 00:42:07,290
So if we add up all the bonds
broken, what we end up with is

891
00:42:07,290 --> 00:42:11,790
12,452 kilojoules per mole,
and it's talking about per

892
00:42:11,790 --> 00:42:14,350
mole of glucose that's
oxidized.

893
00:42:14,350 --> 00:42:17,850
And in terms of bonds formed,
what we see is 15,192

894
00:42:17,850 --> 00:42:21,740
kilojoules per mole.

895
00:42:21,740 --> 00:42:27,190
So all we need to do to figure
out the change in enthalpy,

896
00:42:27,190 --> 00:42:30,380
and when it has this subscript
r here, I meant to mention,

897
00:42:30,380 --> 00:42:32,740
that means the enthalpy
for the reaction.

898
00:42:32,740 --> 00:42:38,290
We just subtract these bonds
here from the ones that we

899
00:42:38,290 --> 00:42:40,480
ended up forming.

900
00:42:40,480 --> 00:42:44,570
So basically, what we're saying
-- excuse me, these are

901
00:42:44,570 --> 00:42:45,660
the ones that we broke.

902
00:42:45,660 --> 00:42:51,480
It's 12,452 minus 15,192,
which we formed.

903
00:42:51,480 --> 00:42:55,370
So we end up with an enthalpy of
reaction of negative 2,740

904
00:42:55,370 --> 00:43:01,090
kilojoules per mole of glucose
that's oxidized.

905
00:43:01,090 --> 00:43:03,570
All right, so if you remember
the number that I told you

906
00:43:03,570 --> 00:43:08,240
before, it doesn't exactly match
up with what we had said

907
00:43:08,240 --> 00:43:09,250
is the exact number.

908
00:43:09,250 --> 00:43:12,400
The exact number is 2,816.

909
00:43:12,400 --> 00:43:15,200
It is within 3% though,
that's pretty good.

910
00:43:15,200 --> 00:43:18,020
Because remember, we're not
using exact bond enthalpies

911
00:43:18,020 --> 00:43:21,160
here, what we were using is
average bond enthalpies.

912
00:43:21,160 --> 00:43:24,180
So it makes sense that we're
going to be a little bit off.

913
00:43:24,180 --> 00:43:27,610
But if all you have in front of
you is the information on

914
00:43:27,610 --> 00:43:30,270
bond enthalpies, mean bond
enthalpies, this is a great

915
00:43:30,270 --> 00:43:33,530
way to figure out the enthalpy
of an overall reaction.

916
00:43:33,530 --> 00:43:35,990
We can think of a different way,
however, to think about

917
00:43:35,990 --> 00:43:38,460
the enthalpy of an overall
reaction, and this is talking

918
00:43:38,460 --> 00:43:41,460
about the heat of formation.

919
00:43:41,460 --> 00:43:45,680
And the heat of formation or
delta h formation here is

920
00:43:45,680 --> 00:43:49,680
equal to the heat of -- or the
enthalpy of reaction, if we're

921
00:43:49,680 --> 00:43:54,420
talking about forming one mole
of compound from its pure

922
00:43:54,420 --> 00:43:56,850
elements, which are in their
standard states.

923
00:43:56,850 --> 00:43:59,340
So basically, there's a table
that you can look up which

924
00:43:59,340 --> 00:44:02,770
tells you the enthalpy of
formation for any compound

925
00:44:02,770 --> 00:44:05,100
that you're interested in, and
this is actually an appendix

926
00:44:05,100 --> 00:44:08,340
to of your textbooks, and you
will need to use this to solve

927
00:44:08,340 --> 00:44:10,630
your problems on p-set.

928
00:44:10,630 --> 00:44:14,390
But let me say that, for
example, if we're talking

929
00:44:14,390 --> 00:44:18,170
about water here, that's formed
from hydrogen and

930
00:44:18,170 --> 00:44:20,390
oxygen, if we're talking about
the elements in their pure

931
00:44:20,390 --> 00:44:26,050
forms at one bar, standard
states, and room temperature.

932
00:44:26,050 --> 00:44:28,600
And if we look this up in our
textbook, we would find that

933
00:44:28,600 --> 00:44:32,610
the delta h of formation for
water is negative 286

934
00:44:32,610 --> 00:44:35,800
kilojoules per mole.

935
00:44:35,800 --> 00:44:38,440
Similarly we can look up the
same thing, for example, for

936
00:44:38,440 --> 00:44:42,590
carbon dioxide, and what we'll
find here is that our delta h

937
00:44:42,590 --> 00:44:46,050
of formation that we look
up is negative 393 .

938
00:44:46,050 --> 00:44:48,940
5 kilojoules per mole.

939
00:44:48,940 --> 00:44:51,850
We can also look up or think
about what our delta h of

940
00:44:51,850 --> 00:44:53,940
formation would be for oxygen.

941
00:44:53,940 --> 00:44:57,080
Does anyone have a guess here?

942
00:44:57,080 --> 00:44:58,990
Yup, it's actually
going to be zero.

943
00:44:58,990 --> 00:45:02,800
Oxygen already is in its most
stable state, so any time

944
00:45:02,800 --> 00:45:05,520
we're talking about an element
in their most stable state,

945
00:45:05,520 --> 00:45:06,690
it's going to be zero.

946
00:45:06,690 --> 00:45:09,040
That's going to be the delta
h of formation, there

947
00:45:09,040 --> 00:45:11,650
is none, it's zero.

948
00:45:11,650 --> 00:45:15,820
We can also look up what it was
for sugar, for glucose, c

949
00:45:15,820 --> 00:45:18,050
6 h 12 o 6.

950
00:45:18,050 --> 00:45:22,406
So that coming from its most
stable forms, it was the most

951
00:45:22,406 --> 00:45:25,880
pure form of the elements, is
going to be negative 1260

952
00:45:25,880 --> 00:45:27,600
kilojoules per mole.

953
00:45:27,600 --> 00:45:31,060
All of this information has
been tabulated and is in

954
00:45:31,060 --> 00:45:33,380
tables, you can refer to them,
and they're also in the back

955
00:45:33,380 --> 00:45:35,940
of your textbook, so you can
refer to those in terms of

956
00:45:35,940 --> 00:45:37,370
your problem-set.

957
00:45:37,370 --> 00:45:40,410
So let's go ahead and solve a
problem actually using the

958
00:45:40,410 --> 00:45:42,030
delta h's of formation.

959
00:45:42,030 --> 00:45:45,100
Let's see if we can do any
better to coming close to the

960
00:45:45,100 --> 00:45:47,620
reality for the oxidation
of glucose.

961
00:45:47,620 --> 00:45:50,970
So if we're going to calculate
the delta h for the reaction

962
00:45:50,970 --> 00:45:54,500
for the oxidation of glucose,
or actually for any reaction

963
00:45:54,500 --> 00:45:58,370
at all, what we want to do is
take the delta h of formation

964
00:45:58,370 --> 00:46:02,280
of the products and subtract
from that the delta h of

965
00:46:02,280 --> 00:46:03,340
formation of the reactants.

966
00:46:03,340 --> 00:46:08,000
So let's go ahead and do that.

967
00:46:08,000 --> 00:46:12,940
And in terms of talking about
the oxidation of glucose, if

968
00:46:12,940 --> 00:46:19,410
we talk about delta h of this
reaction, what we need to take

969
00:46:19,410 --> 00:46:25,350
is 6 times delta h of formation
of c o 2, since

970
00:46:25,350 --> 00:46:28,450
we're forming, that's in our
products, we're forming six

971
00:46:28,450 --> 00:46:30,780
moles of c o 2.

972
00:46:30,780 --> 00:46:38,120
Plus 6 times delta h formation
of h 2 o, since we're forming

973
00:46:38,120 --> 00:46:41,510
six moles of h 2 o.

974
00:46:41,510 --> 00:46:45,450
And we subtract from that the
heat of formation of all of

975
00:46:45,450 --> 00:46:47,260
our reactants.

976
00:46:47,260 --> 00:46:51,640
So we only have one mole, so we
just say delta h formation

977
00:46:51,640 --> 00:46:59,770
of c 6 h 12 o 6, and then in
addition to that we have six

978
00:46:59,770 --> 00:47:07,760
moles delta h formation
of oxygen, of o 2.

979
00:47:07,760 --> 00:47:10,030
All right, so this is our
equation here and at this

980
00:47:10,030 --> 00:47:13,310
point what we would do is we
would look up what all of the

981
00:47:13,310 --> 00:47:17,150
delta h formation values
are for c o 2, h 2

982
00:47:17,150 --> 00:47:21,720
o, sugar, and oxygen.

983
00:47:21,720 --> 00:47:27,910
So what we would find is that
we end up having 6 times

984
00:47:27,910 --> 00:47:30,150
negative 393 .

985
00:47:30,150 --> 00:47:32,530
5 -- that's what we had
just looked up and

986
00:47:32,530 --> 00:47:35,030
told you for c o 2.

987
00:47:35,030 --> 00:47:39,280
Plus 6 times negative 285 .

988
00:47:39,280 --> 00:47:41,400
8 for the water.

989
00:47:41,400 --> 00:47:51,200
Minus 1 times 1260, so
it's negative 1260

990
00:47:51,200 --> 00:47:54,430
for our sugar here.

991
00:47:54,430 --> 00:47:57,570
And then what we're going to end
up with is having minus,

992
00:47:57,570 --> 00:48:00,270
and what is it for
oxygen again?

993
00:48:00,270 --> 00:48:03,220
So minus 0.

994
00:48:03,220 --> 00:48:06,620
So what we end up with in terms
of the delta h for the

995
00:48:06,620 --> 00:48:10,820
entire reaction here, is we end
up with negative 2816, and

996
00:48:10,820 --> 00:48:21,920
it's going to be kilojoules
per mole of glucose.

997
00:48:21,920 --> 00:48:25,960
All right, so let's see how this
matches up, and hopefully

998
00:48:25,960 --> 00:48:28,860
you can actually remember that
this matches up actually

999
00:48:28,860 --> 00:48:30,510
perfectly here.

1000
00:48:30,510 --> 00:48:34,450
So what we are going to see
is that, in fact, what we

1001
00:48:34,450 --> 00:48:36,630
calculated versus what
is experimental

1002
00:48:36,630 --> 00:48:38,100
is dead-on the same.

1003
00:48:38,100 --> 00:48:40,630
So there's actually one more
way to figure out the

1004
00:48:40,630 --> 00:48:42,780
enthalpies of a reaction,
I'm going to go over

1005
00:48:42,780 --> 00:48:44,510
it just very briefly.

1006
00:48:44,510 --> 00:48:47,510
And that's based on the fact
that enthalpy is a state

1007
00:48:47,510 --> 00:48:51,280
function, and by state function
what I mean is that

1008
00:48:51,280 --> 00:48:56,220
it doesn't matter how you got
from point a to point b, all

1009
00:48:56,220 --> 00:48:58,740
that matters is the difference
between the two.

1010
00:48:58,740 --> 00:49:02,030
So another example of a state
function is altitude, for

1011
00:49:02,030 --> 00:49:03,120
example, on a mountain.

1012
00:49:03,120 --> 00:49:06,440
So if you're talking about
altitude, you go from point a

1013
00:49:06,440 --> 00:49:11,060
to point b on the mountain, and
it doesn't matter how you

1014
00:49:11,060 --> 00:49:13,960
got there -- you could have
climbed all the way up the top

1015
00:49:13,960 --> 00:49:16,050
of the mountain, then went
back down and eventually

1016
00:49:16,050 --> 00:49:17,400
landed on point b.

1017
00:49:17,400 --> 00:49:18,990
Or you could have gone
straight from

1018
00:49:18,990 --> 00:49:20,630
point a to point b.

1019
00:49:20,630 --> 00:49:24,000
The change in altitude between
point a and point b do not

1020
00:49:24,000 --> 00:49:26,890
depend on the path, they're
independent of path.

1021
00:49:26,890 --> 00:49:29,960
So this difference right here
does not matter on how you got

1022
00:49:29,960 --> 00:49:32,600
there, it does not make a
difference how you got there,

1023
00:49:32,600 --> 00:49:35,650
altitude is a state function.

1024
00:49:35,650 --> 00:49:38,810
So similarly, we can say that
enthalpy is a state function

1025
00:49:38,810 --> 00:49:43,290
as well, if we're talking about
part reaction a here,

1026
00:49:43,290 --> 00:49:47,770
which has our reactants going
to our products in 2 b here.

1027
00:49:47,770 --> 00:49:49,900
It doesn't matter how
we got there.

1028
00:49:49,900 --> 00:49:52,550
We can actually calculate the
change in enthalpy at all

1029
00:49:52,550 --> 00:49:53,860
different points here.

1030
00:49:53,860 --> 00:49:56,840
All that we actually have to
worry about at the end of the

1031
00:49:56,840 --> 00:49:59,510
day is the difference
between a and b.

1032
00:49:59,510 --> 00:50:02,320
So that's what we mean
by state function.

1033
00:50:02,320 --> 00:50:04,440
Actually, we're not going to
have a chance to get to fully

1034
00:50:04,440 --> 00:50:07,950
explaining the consequence of
this, which is Hess's law,

1035
00:50:07,950 --> 00:50:11,930
which allows us to add and
subtract different reactions.

1036
00:50:11,930 --> 00:50:14,880
So what I'm going to say is the
last two problems on your

1037
00:50:14,880 --> 00:50:17,580
problem-set you won't have to do
because we're not going to

1038
00:50:17,580 --> 00:50:20,230
get a chance to cover
in class on Friday.

1039
00:50:20,230 --> 00:50:24,270
So I'll send out an email about
this as well, so that'll

1040
00:50:24,270 --> 00:50:25,940
be pushed back.

1041
00:50:25,940 --> 00:50:29,070
So, it will be on the exam, so
you want to do them at some

1042
00:50:29,070 --> 00:50:31,350
point, but you don't need to
actually turn those in.

1043
00:50:31,350 --> 00:50:34,260
So those are the last two
problems, I believe.