1 00:00:00,090 --> 00:00:02,430 The following content is provided under a Creative 2 00:00:02,430 --> 00:00:03,820 Commons license. 3 00:00:03,820 --> 00:00:06,060 Your support will help MIT OpenCourseWare 4 00:00:06,060 --> 00:00:10,150 continue to offer high-quality educational resources for free. 5 00:00:10,150 --> 00:00:12,690 To make a donation or to view additional materials 6 00:00:12,690 --> 00:00:16,445 from hundreds of MIT courses, visit MIT OpenCourseWare 7 00:00:16,445 --> 00:00:17,070 at ocw.mit.edu. 8 00:00:26,410 --> 00:00:29,290 CATHERINE DRENNAN: So problems set 5 was due now. 9 00:00:29,290 --> 00:00:31,330 And problem set 6 is due next week. 10 00:00:31,330 --> 00:00:33,440 It will be posted later today. 11 00:00:33,440 --> 00:00:34,750 Welcome to the parents. 12 00:00:34,750 --> 00:00:36,670 We will have clickers too. 13 00:00:36,670 --> 00:00:38,860 Thank you for coming. 14 00:00:38,860 --> 00:00:40,840 So today's topic, we're continuing 15 00:00:40,840 --> 00:00:42,564 with chemical equilibrium. 16 00:00:42,564 --> 00:00:44,230 And depending on when the clickers come, 17 00:00:44,230 --> 00:00:46,810 the fun video may be at the top of the lecture. 18 00:00:46,810 --> 00:00:51,820 But before that, today is going to be a clicker competition. 19 00:00:51,820 --> 00:00:55,030 And hopefully, for the parents in the room, 20 00:00:55,030 --> 00:01:00,910 your child has told you what these clicker competitions are. 21 00:01:00,910 --> 00:01:03,820 The parents will be in their own recitation. 22 00:01:03,820 --> 00:01:07,480 If you win, I think you have to come back next week for snacks 23 00:01:07,480 --> 00:01:09,580 at recitation. 24 00:01:09,580 --> 00:01:11,880 So we'll explain that. 25 00:01:11,880 --> 00:01:16,210 But some recitations have been doing very well in the clicker 26 00:01:16,210 --> 00:01:20,950 competition, but they have not won. 27 00:01:20,950 --> 00:01:25,085 So I just want to share with you another extra-credit clicker 28 00:01:25,085 --> 00:01:25,585 assignment. 29 00:01:28,210 --> 00:01:30,400 And this extra-credit clicker assignment 30 00:01:30,400 --> 00:01:33,460 is something you can do this weekend with your parents. 31 00:01:33,460 --> 00:01:35,500 So again this is optional. 32 00:01:35,500 --> 00:01:41,170 This is to win for your recitation extra-credit points 33 00:01:41,170 --> 00:01:44,590 to get into the championship at the end of the semester 34 00:01:44,590 --> 00:01:46,400 to win the geeky T-shirt. 35 00:01:46,400 --> 00:01:53,200 The geeky T-shirt is itself a prize, or a extra-credit thing 36 00:01:53,200 --> 00:01:55,030 to get in. 37 00:01:55,030 --> 00:01:56,740 OK. 38 00:01:56,740 --> 00:02:01,360 So in class, I have been showing science videos. 39 00:02:01,360 --> 00:02:03,930 And these are the stars of the science videos. 40 00:02:03,930 --> 00:02:07,000 They're MIT undergrads, graduate students, post-docs, 41 00:02:07,000 --> 00:02:08,289 and faculty. 42 00:02:08,289 --> 00:02:11,170 And they've been talking about how they use basic chemical 43 00:02:11,170 --> 00:02:13,840 principles in their research and how 44 00:02:13,840 --> 00:02:15,970 that research is important for addressing 45 00:02:15,970 --> 00:02:17,900 a real-world problem. 46 00:02:17,900 --> 00:02:19,990 So the extra credit assignment is 47 00:02:19,990 --> 00:02:22,030 that each of these individuals also 48 00:02:22,030 --> 00:02:25,100 has a two to-- I think the longest one is about-- 49 00:02:25,100 --> 00:02:28,150 five-minute personal video. 50 00:02:28,150 --> 00:02:31,600 And so the extra credit assignment 51 00:02:31,600 --> 00:02:35,860 is to watch one or all, as many as you want, 52 00:02:35,860 --> 00:02:38,260 of these personal videos, and then 53 00:02:38,260 --> 00:02:41,920 send Allena an e-mail with your recitation 54 00:02:41,920 --> 00:02:45,820 number in the subject line saying one thing that surprised 55 00:02:45,820 --> 00:02:47,990 you in a personal video or one thing 56 00:02:47,990 --> 00:02:49,540 to which you could really relate, 57 00:02:49,540 --> 00:02:51,430 that someone said in their personal video. 58 00:02:51,430 --> 00:02:53,140 So it can just be one or two sentences. 59 00:02:53,140 --> 00:02:54,850 It doesn't have to be long. 60 00:02:54,850 --> 00:02:56,950 When I gave this assignment before, 61 00:02:56,950 --> 00:03:00,700 I'll give you a little help on where you might want to start. 62 00:03:00,700 --> 00:03:04,060 We had the most comments about Ben's personal video 63 00:03:04,060 --> 00:03:06,070 and Samuel's personal video. 64 00:03:06,070 --> 00:03:09,430 And some people also commented on my personal video. 65 00:03:09,430 --> 00:03:11,680 So these are personal videos that kind of 66 00:03:11,680 --> 00:03:15,410 tell people's path to science or people's path to chemistry. 67 00:03:15,410 --> 00:03:15,910 So 68 00:03:15,910 --> 00:03:17,890 I thought this might be a fun thing to do. 69 00:03:17,890 --> 00:03:20,170 It's available online here. 70 00:03:20,170 --> 00:03:22,690 You can watch some of these- again, two-to-five-minutes-- 71 00:03:22,690 --> 00:03:23,830 with your parents. 72 00:03:23,830 --> 00:03:27,310 And that might also help your parents understand a little 73 00:03:27,310 --> 00:03:29,980 about the people who are here at MIT. 74 00:03:29,980 --> 00:03:32,470 So this is something, and it's due November 3. 75 00:03:32,470 --> 00:03:34,550 But I thought it might be a fun thing 76 00:03:34,550 --> 00:03:36,940 to do homework with their parents on visiting weekend. 77 00:03:36,940 --> 00:03:39,490 That's an awesome thing to be able to do. 78 00:03:39,490 --> 00:03:40,360 All right. 79 00:03:40,360 --> 00:03:41,950 So clicker competition. 80 00:03:41,950 --> 00:03:46,240 Recitations 7-- Dan must unseat him. 81 00:03:46,240 --> 00:03:48,580 Here's one that parents might know the answer to. 82 00:03:48,580 --> 00:03:49,990 We'll see. 83 00:03:49,990 --> 00:03:51,860 And again, you can share. 84 00:03:51,860 --> 00:03:54,627 But remember, your parents are competing against you. 85 00:03:59,500 --> 00:04:00,530 All right. 86 00:04:00,530 --> 00:04:02,640 Let's just try 10 more seconds. 87 00:04:17,230 --> 00:04:17,982 Very good. 88 00:04:24,910 --> 00:04:28,210 So that's the answer. 89 00:04:28,210 --> 00:04:29,830 So that was yesterday. 90 00:04:29,830 --> 00:04:33,970 And so this, every year, it's National Chemistry Week 91 00:04:33,970 --> 00:04:36,010 on the week of Mole Day. 92 00:04:36,010 --> 00:04:38,170 So this is national chemistry week. 93 00:04:38,170 --> 00:04:41,296 So if I can get most of the way through lecture, 94 00:04:41,296 --> 00:04:42,670 I'm going to share with you a fun 95 00:04:42,670 --> 00:04:45,970 video at the end that celebrates national chemistry week. 96 00:04:45,970 --> 00:04:47,320 So hopefully we'll get there. 97 00:04:47,320 --> 00:04:49,720 But first, let's talk a little bit 98 00:04:49,720 --> 00:04:53,950 about chemical equilibrium, the subject for today. 99 00:04:53,950 --> 00:05:00,050 So chemical equilibrium-- it's all about staying calm. 100 00:05:00,050 --> 00:05:04,640 So we want the rate in to be equal to the rate out. 101 00:05:04,640 --> 00:05:07,790 We like to be at this equilibrium place. 102 00:05:07,790 --> 00:05:11,690 But sometimes, often, all the time-- frankly, all the time, 103 00:05:11,690 --> 00:05:15,530 stress is applied to our equilibrium situation. 104 00:05:15,530 --> 00:05:20,090 And systems must respond in such a way to alleviate that stress. 105 00:05:20,090 --> 00:05:23,090 So Le Chatelier's principle suggests 106 00:05:23,090 --> 00:05:25,370 that, when a stress is applied to the system, 107 00:05:25,370 --> 00:05:29,660 the system will respond in such a way to minimize the stress. 108 00:05:29,660 --> 00:05:33,210 Again, this is about keeping calm, minimizing stress. 109 00:05:33,210 --> 00:05:36,260 And if you think about what direction the reaction will 110 00:05:36,260 --> 00:05:40,010 go to minimize the stress, you can predict 111 00:05:40,010 --> 00:05:42,570 the direction of the reaction. 112 00:05:42,570 --> 00:05:46,357 So today, we're going to talk about some of the stresses 113 00:05:46,357 --> 00:05:46,940 to the system. 114 00:05:46,940 --> 00:05:49,010 Last time, we talked about adding and removing 115 00:05:49,010 --> 00:05:50,540 reactants and products. 116 00:05:50,540 --> 00:05:52,940 This time, we're going to talk about gases. 117 00:05:52,940 --> 00:05:55,610 And we're going to talk about changing the volume. 118 00:05:55,610 --> 00:05:58,800 That's our first stress to the system. 119 00:05:58,800 --> 00:06:02,580 So if you decrease the volume of a gaseous system, 120 00:06:02,580 --> 00:06:06,750 it will cause an increase in the total pressure. 121 00:06:06,750 --> 00:06:10,520 And we know this from the ideal gas law 122 00:06:10,520 --> 00:06:14,240 and other relationships also between pressure and volume. 123 00:06:14,240 --> 00:06:16,370 So the ideal gas law is something 124 00:06:16,370 --> 00:06:19,070 most MIT students are familiar with, because it 125 00:06:19,070 --> 00:06:23,540 is, in fact, the T in MIT. 126 00:06:23,540 --> 00:06:27,230 So PV equals nRT. 127 00:06:27,230 --> 00:06:33,380 where P is pressure, V is volume, T is temperature, 128 00:06:33,380 --> 00:06:36,560 n is the number of moles of that ideal gas, 129 00:06:36,560 --> 00:06:39,180 and R is our ideal gas constant. 130 00:06:39,180 --> 00:06:41,900 So this relates pressure to volume 131 00:06:41,900 --> 00:06:45,950 at a constant temperature and relates pressure, volume, 132 00:06:45,950 --> 00:06:49,880 and temperature and also number of moles to reach other. 133 00:06:49,880 --> 00:06:52,340 So this is a very important expression, 134 00:06:52,340 --> 00:06:55,520 and we won't actually be talking very much about the ideal gas 135 00:06:55,520 --> 00:06:56,120 law. 136 00:06:56,120 --> 00:06:58,610 But you need it in this unit, because in this unit, 137 00:06:58,610 --> 00:07:01,760 we're thinking about stresses to equilibrium situations 138 00:07:01,760 --> 00:07:05,070 and how reactions are going to respond. 139 00:07:05,070 --> 00:07:09,240 So if you decrease the volume of a gaseous system, 140 00:07:09,240 --> 00:07:11,930 causing an increase in total pressure, 141 00:07:11,930 --> 00:07:17,120 the system's going to respond in such way to minimize the stress 142 00:07:17,120 --> 00:07:20,450 or decrease the total pressure. 143 00:07:20,450 --> 00:07:22,190 And so Le Chatelier's principle would 144 00:07:22,190 --> 00:07:24,980 predict that, if possible, the system's 145 00:07:24,980 --> 00:07:28,950 going to respond in such a way to reduce that total pressure. 146 00:07:28,950 --> 00:07:32,030 So you increase the pressure, reduce the pressure. 147 00:07:32,030 --> 00:07:34,670 Minimize the stress. 148 00:07:34,670 --> 00:07:40,010 So let's look at a reaction of a gas to another gas. 149 00:07:40,010 --> 00:07:43,100 So here we have the molecules of gas P2 150 00:07:43,100 --> 00:07:46,430 going to one molecule of P4. 151 00:07:46,430 --> 00:07:50,210 And if we had a container with a particular volume 152 00:07:50,210 --> 00:07:56,090 and we compress that volume, the reaction that is at equilibrium 153 00:07:56,090 --> 00:07:58,670 is going to respond. 154 00:07:58,670 --> 00:08:02,840 And here, a decrease in volume is 155 00:08:02,840 --> 00:08:07,250 going to shift the reaction toward product. 156 00:08:07,250 --> 00:08:08,480 So why is this? 157 00:08:08,480 --> 00:08:11,510 Why is it going to shift it toward product? 158 00:08:11,510 --> 00:08:16,250 And it's because, for every two molecules of P2 159 00:08:16,250 --> 00:08:22,220 that are consumed, only one molecule of P4 is formed. 160 00:08:22,220 --> 00:08:27,770 And thus, the shift toward product, shift toward P4, 161 00:08:27,770 --> 00:08:30,470 is going to reduce the total pressure, because you 162 00:08:30,470 --> 00:08:32,900 have fewer molecules of gas. 163 00:08:32,900 --> 00:08:37,429 So each of them is a little bit happier in this now decreased 164 00:08:37,429 --> 00:08:39,110 Volume 165 00:08:39,110 --> 00:08:42,570 So you can also just think about what direction, 166 00:08:42,570 --> 00:08:44,670 where are the moles, and how this is shifting. 167 00:08:44,670 --> 00:08:49,160 But you can also think about this in terms of Q and K, 168 00:08:49,160 --> 00:08:50,720 and I highly recommend this. 169 00:08:50,720 --> 00:08:53,480 I'm a big fan of thinking about the relationship between Q 170 00:08:53,480 --> 00:08:57,790 and K. So let's think about this now. 171 00:08:57,790 --> 00:09:00,620 Let's just suppose that the volume 172 00:09:00,620 --> 00:09:04,200 is decreased by a factor of 2. 173 00:09:04,200 --> 00:09:06,680 So we were at equilibrium. 174 00:09:06,680 --> 00:09:09,680 Q was equal to K. K is the equilibrium 175 00:09:09,680 --> 00:09:12,350 constant, or the reaction quotient, at equilibrium. 176 00:09:12,350 --> 00:09:16,130 But now, we have changed the volume by 2. 177 00:09:16,130 --> 00:09:19,940 So we can think about what has happened to Q. 178 00:09:19,940 --> 00:09:25,640 So Q is products over reactants at any time point. 179 00:09:25,640 --> 00:09:29,270 Product is the partial pressure of gas P4-- 180 00:09:29,270 --> 00:09:32,510 that's our product-- over the partial pressure 181 00:09:32,510 --> 00:09:35,990 of the reactants, the partial pressure of P2 gas. 182 00:09:35,990 --> 00:09:37,580 But there are two of them, so we have 183 00:09:37,580 --> 00:09:40,590 to remember the stoichiometry of the reaction. 184 00:09:40,590 --> 00:09:43,430 So both of these are affected. 185 00:09:43,430 --> 00:09:46,760 But because of the stoichiometry of the reaction, 186 00:09:46,760 --> 00:09:48,810 Q is now a half. 187 00:09:48,810 --> 00:09:51,360 So Q has changed. 188 00:09:51,360 --> 00:09:55,860 We have decreased Q by a factor of 2. 189 00:09:55,860 --> 00:10:03,650 So Q is now less than K. So tell me what happens to delta G 190 00:10:03,650 --> 00:10:04,600 in this situation. 191 00:10:25,520 --> 00:10:26,990 Let's try just 10 more seconds. 192 00:10:42,665 --> 00:10:44,400 Yep. 193 00:10:44,400 --> 00:10:49,690 So it is a negative value, and let's take a look at why. 194 00:10:49,690 --> 00:10:52,890 So delta G is negative. 195 00:10:52,890 --> 00:10:59,340 And we recall this relationship that delta G RT natural log 196 00:10:59,340 --> 00:11:04,140 of Q over K. So when Q is less than K, 197 00:11:04,140 --> 00:11:07,590 you get a negative value for delta G. 198 00:11:07,590 --> 00:11:11,070 And when you have a negative value for delta G, 199 00:11:11,070 --> 00:11:13,840 the reaction goes in the forward direction. 200 00:11:13,840 --> 00:11:15,810 So a negative value for delta G means 201 00:11:15,810 --> 00:11:18,180 it's spontaneous in the forward direction. 202 00:11:18,180 --> 00:11:20,580 The forward direction is toward products. 203 00:11:20,580 --> 00:11:23,910 And this will happen until Q equals K again. 204 00:11:23,910 --> 00:11:26,550 So you can think about this based on the equation. 205 00:11:26,550 --> 00:11:28,920 Always ask yourself, this Q changing? 206 00:11:28,920 --> 00:11:31,710 Is Q less than K or greater than K? 207 00:11:31,710 --> 00:11:34,560 And that'll predict the direction to which 208 00:11:34,560 --> 00:11:37,750 the reaction will switch. 209 00:11:37,750 --> 00:11:40,740 So it's going to go in the forward direction 210 00:11:40,740 --> 00:11:43,440 if delta G is negative. 211 00:11:43,440 --> 00:11:44,880 All right. 212 00:11:44,880 --> 00:11:47,610 Now let's increase the volume and think about what 213 00:11:47,610 --> 00:11:48,820 happens in the container. 214 00:11:48,820 --> 00:11:50,250 So we have a container here. 215 00:11:50,250 --> 00:11:53,400 We increase the volume. 216 00:11:53,400 --> 00:11:56,190 So now, we're going to shift to the reaction 217 00:11:56,190 --> 00:11:58,590 toward our reactants. 218 00:11:58,590 --> 00:12:00,690 So the increase in volume is going 219 00:12:00,690 --> 00:12:03,090 to lower that total pressure. 220 00:12:03,090 --> 00:12:05,610 And we can think about this switch. 221 00:12:05,610 --> 00:12:09,930 We have one molecule of P4 on the products, 222 00:12:09,930 --> 00:12:12,210 two molecules of P2 here. 223 00:12:12,210 --> 00:12:15,000 So for every one molecule consumed 224 00:12:15,000 --> 00:12:20,140 in the backward direction, two molecules of P2 are formed. 225 00:12:20,140 --> 00:12:27,630 So the shift will compensate for this change, 226 00:12:27,630 --> 00:12:30,390 and we're going to increase the delta pressure, which 227 00:12:30,390 --> 00:12:34,170 was decreased before, by this increase in volume. 228 00:12:34,170 --> 00:12:36,510 So again, you're shifting it in such a way 229 00:12:36,510 --> 00:12:38,550 to minimize the stress. 230 00:12:38,550 --> 00:12:42,960 Even if the stress is a decrease in pressure, 231 00:12:42,960 --> 00:12:45,150 you want to be back at your equilibrium place. 232 00:12:45,150 --> 00:12:50,670 So you'll shift to then increase the total pressure just 233 00:12:50,670 --> 00:12:53,250 to compensate in any way, minimize the stress. 234 00:12:53,250 --> 00:12:56,280 Whatever the stress is, you want to minimize it. 235 00:12:56,280 --> 00:12:57,910 All right. 236 00:12:57,910 --> 00:13:01,050 Let's do something slightly trickier. 237 00:13:01,050 --> 00:13:05,560 Let's add an inert gas to this reaction. 238 00:13:05,560 --> 00:13:08,490 So we're going to add an inert gas to a container, 239 00:13:08,490 --> 00:13:13,080 increasing the total pressure at constant temperature. 240 00:13:13,080 --> 00:13:15,341 Why don't you predict what's going to happen? 241 00:13:31,750 --> 00:13:33,090 All right, 10 more seconds. 242 00:13:51,820 --> 00:13:54,010 Yes, this is a tricky one. 243 00:13:54,010 --> 00:13:56,125 Since it's a clicker competition, we won't repoll, 244 00:13:56,125 --> 00:13:58,110 and we'll put up the answer. 245 00:13:58,110 --> 00:14:00,168 Ooh, by a slight edge. 246 00:14:03,320 --> 00:14:07,360 So this seems very counter-intuitive, so let's 247 00:14:07,360 --> 00:14:09,520 discuss it. 248 00:14:09,520 --> 00:14:11,080 So nothing happens. 249 00:14:11,080 --> 00:14:14,040 But why? 250 00:14:14,040 --> 00:14:19,750 So Q depends on the partial pressure of these gases. 251 00:14:19,750 --> 00:14:23,020 And under the scenario described here, 252 00:14:23,020 --> 00:14:26,110 the partial pressures were actually not changing. 253 00:14:26,110 --> 00:14:27,760 So Q was not changing. 254 00:14:27,760 --> 00:14:30,160 And therefore, there was no shift. 255 00:14:30,160 --> 00:14:33,010 So to understand this, we have to do a little partial pressure 256 00:14:33,010 --> 00:14:35,230 review. 257 00:14:35,230 --> 00:14:38,550 So partial pressure of gases. 258 00:14:38,550 --> 00:14:40,630 The partial pressure is the pressure 259 00:14:40,630 --> 00:14:44,920 that each gas would exert if it were by itself. 260 00:14:44,920 --> 00:14:47,480 That's the definition of partial pressure. 261 00:14:47,480 --> 00:14:51,610 So if we have oxygen at one atmosphere and nitrogen 262 00:14:51,610 --> 00:14:54,970 at one atmosphere, and you add them together, 263 00:14:54,970 --> 00:14:58,540 and now you have a total pressure of two atmospheres-- 1 264 00:14:58,540 --> 00:15:03,070 plus 1 equals 2-- but the partial pressure of O2 265 00:15:03,070 --> 00:15:06,700 here is identical to its partial pressure 266 00:15:06,700 --> 00:15:10,790 here, its partial pressure as if it was there by itself. 267 00:15:10,790 --> 00:15:13,240 It has no interest in this inert gas. 268 00:15:13,240 --> 00:15:16,900 It ignores it and feels no different as a result of it. 269 00:15:16,900 --> 00:15:22,390 Very just sort of isolationist with these ideal gases. 270 00:15:22,390 --> 00:15:26,020 So the partial pressure of O2 here is the same. 271 00:15:26,020 --> 00:15:27,880 And so we can look mathematically 272 00:15:27,880 --> 00:15:29,260 at this expression. 273 00:15:29,260 --> 00:15:31,900 So the partial pressure of gas A is 274 00:15:31,900 --> 00:15:37,390 equal to the number of moles of that gas, RT over volume. 275 00:15:37,390 --> 00:15:40,660 The total pressure is equal to the partial pressure 276 00:15:40,660 --> 00:15:44,590 of gas ABC, how many ever gases there are. 277 00:15:44,590 --> 00:15:48,220 But the partial pressure of each gas, like O2 here, 278 00:15:48,220 --> 00:15:50,890 just depends on the number of moles of that gas 279 00:15:50,890 --> 00:15:53,680 and the volume of that container, 280 00:15:53,680 --> 00:15:56,330 assuming constant temperature. 281 00:15:56,330 --> 00:15:59,650 So if the partial pressure isn't going 282 00:15:59,650 --> 00:16:02,920 to change-- so if you add inert gases, increasing 283 00:16:02,920 --> 00:16:07,990 the total pressure, the partial pressure is unchanged. 284 00:16:07,990 --> 00:16:12,240 And when the partial pressure is unchanged, Q is unchanged. 285 00:16:12,240 --> 00:16:14,560 Remember, Q equals the partial pressure 286 00:16:14,560 --> 00:16:17,200 of the gas products over the partial pressure or the gas 287 00:16:17,200 --> 00:16:18,130 reactants. 288 00:16:18,130 --> 00:16:22,360 So if partial pressures don't change, Q does not change. 289 00:16:22,360 --> 00:16:26,800 And if Q doesn't change, then Q is the same as K, 290 00:16:26,800 --> 00:16:29,200 and there is no shift. 291 00:16:29,200 --> 00:16:32,560 So we have to always ask ourselves, 292 00:16:32,560 --> 00:16:34,120 what's happened to the container? 293 00:16:34,120 --> 00:16:35,440 What's the partial pressure? 294 00:16:35,440 --> 00:16:38,767 Did the partial pressure change? 295 00:16:38,767 --> 00:16:39,850 Let's try another example. 296 00:16:42,400 --> 00:16:44,440 Let's add another inert gas. 297 00:16:44,440 --> 00:16:48,310 But this time, we're going to add it to a container. 298 00:16:48,310 --> 00:16:51,220 And the total pressure and the temperature 299 00:16:51,220 --> 00:16:53,260 are kept constant in this case. 300 00:16:53,260 --> 00:16:55,750 So this is another clicker question. 301 00:16:55,750 --> 00:16:58,345 Why didn't you see what you think is going to happen here? 302 00:17:13,251 --> 00:17:14,750 All right, let's do 10 more seconds. 303 00:17:34,610 --> 00:17:35,906 All right. 304 00:17:35,906 --> 00:17:37,030 This is a good clicker day. 305 00:17:37,030 --> 00:17:41,230 Sometimes whenever the answers are all 90%, 306 00:17:41,230 --> 00:17:45,820 then it's decided that these questions will determine it. 307 00:17:45,820 --> 00:17:49,250 All right, so let's look at this. 308 00:17:49,250 --> 00:17:51,730 So we're going to shift toward reactant. 309 00:17:51,730 --> 00:17:55,370 Again, let's consider why. 310 00:17:55,370 --> 00:17:55,870 All right. 311 00:17:55,870 --> 00:17:59,080 So in this problem, we're adding inert gas. 312 00:17:59,080 --> 00:18:00,940 Total pressure and temperature are constant. 313 00:18:00,940 --> 00:18:03,520 Well, temperature was constant before. 314 00:18:03,520 --> 00:18:07,280 But total pressure wasn't in the last example. 315 00:18:07,280 --> 00:18:10,570 So let's go back to our picture here. 316 00:18:10,570 --> 00:18:15,050 So if the total pressure was to stay constant-- 317 00:18:15,050 --> 00:18:17,770 and normally, if you add, one atmosphere of O2 318 00:18:17,770 --> 00:18:21,340 and one atmosphere of N2, the total pressure 319 00:18:21,340 --> 00:18:23,860 is two atmospheres, because total pressure 320 00:18:23,860 --> 00:18:26,020 equals partial pressure of one gas 321 00:18:26,020 --> 00:18:28,420 plus the partial pressure of the other gas. 322 00:18:28,420 --> 00:18:34,090 So if the total pressure is constant, what has to happen? 323 00:18:34,090 --> 00:18:35,190 Tell me. 324 00:18:35,190 --> 00:18:38,590 What happened? 325 00:18:38,590 --> 00:18:43,610 So the volume must have changed. 326 00:18:43,610 --> 00:18:45,950 So if the temperature stayed the same, 327 00:18:45,950 --> 00:18:48,610 the volume of the container must have increased. 328 00:18:48,610 --> 00:18:52,390 Because otherwise, the pressure, the total pressure, 329 00:18:52,390 --> 00:18:54,640 should have changed. 330 00:18:54,640 --> 00:18:55,840 And it didn't. 331 00:18:55,840 --> 00:18:57,850 So the system was manipulated. 332 00:18:57,850 --> 00:18:59,920 The volume must have increased. 333 00:18:59,920 --> 00:19:01,600 So now, let's think about what happens 334 00:19:01,600 --> 00:19:03,430 when the volume increases. 335 00:19:03,430 --> 00:19:09,605 When the volume increases, the partial pressures decrease, 336 00:19:09,605 --> 00:19:11,230 because they're now in a bigger volume, 337 00:19:11,230 --> 00:19:13,396 because partial pressure depends on number of moles. 338 00:19:13,396 --> 00:19:16,780 It depends on volume at constant temperature. 339 00:19:16,780 --> 00:19:19,420 And so if the partial pressures decrease, 340 00:19:19,420 --> 00:19:23,170 then Q is also going to change. 341 00:19:23,170 --> 00:19:26,710 And when Q changes, the reaction is going to respond. 342 00:19:26,710 --> 00:19:29,440 And in this way, it's going to respond in such a way 343 00:19:29,440 --> 00:19:32,061 that you want to increase the pressure, 344 00:19:32,061 --> 00:19:33,310 because we have this decrease. 345 00:19:33,310 --> 00:19:35,290 So now we want to increase. 346 00:19:35,290 --> 00:19:38,500 And so we're going to switch from one mole to two. 347 00:19:38,500 --> 00:19:43,730 And so the reaction is going to shift toward the reactants. 348 00:19:43,730 --> 00:19:48,610 So in doing these problems with partial pressures and gases, 349 00:19:48,610 --> 00:19:52,330 you always have to ask yourself, did Q change? 350 00:19:52,330 --> 00:19:55,750 And whether Q changed is whether the partial pressures change. 351 00:19:55,750 --> 00:19:57,280 And partial pressure will definitely 352 00:19:57,280 --> 00:20:00,270 change if you change moles or if you change the volume. 353 00:20:00,270 --> 00:20:02,020 So often in these problems, you're saying, 354 00:20:02,020 --> 00:20:03,460 did the volume change? 355 00:20:03,460 --> 00:20:05,710 Volume change, partial pressure change. 356 00:20:05,710 --> 00:20:06,640 Q is different. 357 00:20:06,640 --> 00:20:08,530 The reaction is going to shift. 358 00:20:08,530 --> 00:20:13,120 So there's lots of examples on this in problem set 6. 359 00:20:13,120 --> 00:20:15,670 So you can go work on those. 360 00:20:15,670 --> 00:20:16,750 All right. 361 00:20:16,750 --> 00:20:20,650 So that is about volume. 362 00:20:20,650 --> 00:20:22,420 We've had temperature constant. 363 00:20:22,420 --> 00:20:24,350 Can't do that forever. 364 00:20:24,350 --> 00:20:28,371 Now it's time to change the temperature. 365 00:20:28,371 --> 00:20:28,870 All right. 366 00:20:28,870 --> 00:20:32,050 So changing the temperature of an equilibrium mixture 367 00:20:32,050 --> 00:20:38,200 by adding heat is going to shift the reaction in such a way 368 00:20:38,200 --> 00:20:40,600 that some of that heat is absorbed. 369 00:20:40,600 --> 00:20:44,260 So again, this is consistent with Le Chatelier. 370 00:20:44,260 --> 00:20:46,180 Minimize the stress. 371 00:20:46,180 --> 00:20:48,280 Add heat, absorb heat. 372 00:20:48,280 --> 00:20:50,710 Remove heat, create more heat. 373 00:20:50,710 --> 00:20:54,400 Again, you're minimizing the stress to the system. 374 00:20:54,400 --> 00:20:57,280 So now let's think of different types of reactions. 375 00:20:57,280 --> 00:21:00,370 We have endothermic and exothermic reactions. 376 00:21:00,370 --> 00:21:03,100 And let's think about the effect of changing the temperature 377 00:21:03,100 --> 00:21:05,900 on those reactions. 378 00:21:05,900 --> 00:21:09,130 So let's think about raising the temperature 379 00:21:09,130 --> 00:21:11,830 of an exothermic reaction. 380 00:21:11,830 --> 00:21:13,780 Is that going to shift the formation 381 00:21:13,780 --> 00:21:15,490 of reactants or products? 382 00:21:15,490 --> 00:21:16,285 What do you think? 383 00:21:19,255 --> 00:21:20,740 Reactants. 384 00:21:20,740 --> 00:21:22,447 All right, let's consider why. 385 00:21:26,840 --> 00:21:29,510 So for an exothermic reaction, that 386 00:21:29,510 --> 00:21:32,480 means that the reaction in the forward direction 387 00:21:32,480 --> 00:21:36,020 is exothermic, which also means that the reaction 388 00:21:36,020 --> 00:21:39,320 in the reverse direction is endothermic. 389 00:21:39,320 --> 00:21:41,930 So for an exothermic reaction-- exothermic 390 00:21:41,930 --> 00:21:43,610 in the forward direction-- heat is 391 00:21:43,610 --> 00:21:46,370 produced when you go from reactants to products. 392 00:21:46,370 --> 00:21:49,850 And in the endothermic direction, heat is absorbed. 393 00:21:49,850 --> 00:21:52,340 So if you raise the temperature, you're 394 00:21:52,340 --> 00:21:54,230 going to want to minimize the stress. 395 00:21:54,230 --> 00:21:57,350 So you want to shift it in the endothermic direction. 396 00:21:57,350 --> 00:21:59,210 You want to shift it in the direction 397 00:21:59,210 --> 00:22:02,840 that heat is absorbed, which, in this case, is toward reactants. 398 00:22:06,320 --> 00:22:08,760 Now let's think about an endothermic reaction. 399 00:22:08,760 --> 00:22:11,280 Raising the temperature of an endothermic reaction 400 00:22:11,280 --> 00:22:14,190 is going to shift toward products. 401 00:22:14,190 --> 00:22:16,550 And if we put our pictures again, 402 00:22:16,550 --> 00:22:18,860 an endothermic reaction is endothermic 403 00:22:18,860 --> 00:22:20,290 in the forward direction. 404 00:22:20,290 --> 00:22:23,150 So heat is absorbed from reactants to products. 405 00:22:23,150 --> 00:22:26,420 And in the reverse direction of an endothermic reaction 406 00:22:26,420 --> 00:22:29,390 is the exothermic direction in which heat is produced. 407 00:22:29,390 --> 00:22:31,710 So if you raise the temperature, then you're 408 00:22:31,710 --> 00:22:33,780 going to want to shift in such a direction 409 00:22:33,780 --> 00:22:36,320 to minimize that stress in a direction 410 00:22:36,320 --> 00:22:38,520 to absorb heat, which, in this case, 411 00:22:38,520 --> 00:22:41,490 sends you toward products. 412 00:22:41,490 --> 00:22:46,710 So here, the predictive tool is our friend delta H. 413 00:22:46,710 --> 00:22:49,470 So delta H tells us whether reactions 414 00:22:49,470 --> 00:22:52,530 are exothermic or endothermic, whether delta h is 415 00:22:52,530 --> 00:22:54,150 negative or positive. 416 00:22:54,150 --> 00:22:57,170 So for some things, the prediction 417 00:22:57,170 --> 00:22:59,760 is what's happening to delta G. Here, 418 00:22:59,760 --> 00:23:03,690 our predictive tool is the sine of delta H. 419 00:23:03,690 --> 00:23:06,140 So let's do a clicker question, and tell me 420 00:23:06,140 --> 00:23:09,480 what direction you think this particular reaction is 421 00:23:09,480 --> 00:23:12,570 going to go if you add heat. 422 00:23:23,500 --> 00:23:24,760 All right, 10 more seconds. 423 00:23:39,690 --> 00:23:40,380 All right. 424 00:23:40,380 --> 00:23:44,300 So is this an exo- or endothermic reaction? 425 00:23:44,300 --> 00:23:47,130 Exothermic, because we have the negative sign. 426 00:23:47,130 --> 00:23:49,830 And so then we can think about what's going to happen. 427 00:23:49,830 --> 00:23:51,160 So you add heat. 428 00:23:51,160 --> 00:23:53,260 You're going to want to shift it in the direction 429 00:23:53,260 --> 00:23:54,810 to absorb the heat. 430 00:23:54,810 --> 00:23:56,790 So you're going to shift it toward reactants 431 00:23:56,790 --> 00:24:00,330 in the endothermic direction, absorb the heat. 432 00:24:00,330 --> 00:24:02,710 So again, delta H is the predictive tool. 433 00:24:02,710 --> 00:24:05,620 You have to remember negative delta H exothermic, 434 00:24:05,620 --> 00:24:07,740 positive delta H endothermic. 435 00:24:07,740 --> 00:24:10,180 And then just think about shifting 436 00:24:10,180 --> 00:24:14,800 to minimize the stress, always minimizing the stress. 437 00:24:14,800 --> 00:24:15,300 All right. 438 00:24:19,340 --> 00:24:25,240 So our equilibrium constant K. It's a constant, except that it 439 00:24:25,240 --> 00:24:27,450 changes with temperature. 440 00:24:27,450 --> 00:24:32,840 So the equilibrium constant has a temperature dependence. 441 00:24:32,840 --> 00:24:35,380 So big K, the equilibrium constant, 442 00:24:35,380 --> 00:24:37,640 can change with temperature. 443 00:24:37,640 --> 00:24:40,710 Reaction rates can also change with temperature. 444 00:24:40,710 --> 00:24:42,680 So when we talk about kinetics, we're 445 00:24:42,680 --> 00:24:45,250 going to have little Ks, which are reaction rates. 446 00:24:45,250 --> 00:24:47,990 And they're going to change with temperature as well. 447 00:24:47,990 --> 00:24:51,110 So how does the equilibrium constant 448 00:24:51,110 --> 00:24:53,020 change with temperature? 449 00:24:53,020 --> 00:24:55,660 And you might feel a derivation coming on, 450 00:24:55,660 --> 00:24:57,350 and you would be right. 451 00:24:57,350 --> 00:25:01,460 So let's think about what we know, equations that involve 452 00:25:01,460 --> 00:25:03,350 the equilibrium constant. 453 00:25:03,350 --> 00:25:06,800 We saw before that delta G0 equals minus RT 454 00:25:06,800 --> 00:25:10,420 natural log of K. What else do we 455 00:25:10,420 --> 00:25:14,120 know about delta G0 equations? 456 00:25:14,120 --> 00:25:16,535 What else does delta G0 equal? 457 00:25:16,535 --> 00:25:22,610 It equals our friend delta H not minus T delta S0. 458 00:25:22,610 --> 00:25:27,620 And we can rearrange this expression, 459 00:25:27,620 --> 00:25:31,580 solving for the natural log of K. 460 00:25:31,580 --> 00:25:35,980 And if we assume-- and it's a good assumption-- 461 00:25:35,980 --> 00:25:40,650 that delta H and delta S0 are independent of temperature, 462 00:25:40,650 --> 00:25:46,370 that means that K is going to change with temperature. 463 00:25:46,370 --> 00:25:49,610 And we can think about two different temperatures 464 00:25:49,610 --> 00:25:53,240 and come up with a unified equation. 465 00:25:53,240 --> 00:25:56,440 So if we consider a reaction carried out-- temperature T1 466 00:25:56,440 --> 00:26:01,190 and temperature T2-- we would have natural log of K2 equals 467 00:26:01,190 --> 00:26:06,190 minus delta H0 over R and over temperature 2 468 00:26:06,190 --> 00:26:10,130 plus delta S over R. And we have the same thing now 469 00:26:10,130 --> 00:26:13,420 but for equilibrium constant 1 and temperature 1. 470 00:26:13,420 --> 00:26:17,270 So we can combine these, and things will cancel. 471 00:26:17,270 --> 00:26:21,520 So subtracting those two equations gives you this. 472 00:26:21,520 --> 00:26:23,740 And it's a named equation in chemistry, 473 00:26:23,740 --> 00:26:26,920 which means that it's probably pretty important, because a lot 474 00:26:26,920 --> 00:26:28,550 of things don't have names. 475 00:26:28,550 --> 00:26:31,150 So we have the natural log of the equilibrium 476 00:26:31,150 --> 00:26:35,140 constant K2 over equilibrium constant K1 477 00:26:35,140 --> 00:26:41,140 equals minus delta H0 over R, which 478 00:26:41,140 --> 00:26:46,130 is a constant, in brackets, 1 over temperature 2 minus 1 479 00:26:46,130 --> 00:26:47,950 over temperature 1. 480 00:26:47,950 --> 00:26:49,910 Van 't Hoff equation. 481 00:26:49,910 --> 00:26:51,410 And later in the semester, I'm going 482 00:26:51,410 --> 00:26:54,020 to ask you to recall this equation. 483 00:26:54,020 --> 00:26:56,500 And I'll have a special prize for the first person who 484 00:26:56,500 --> 00:26:59,150 comes up with the Van 't Hoff equation, so you 485 00:26:59,150 --> 00:27:00,520 can keep that in mind. 486 00:27:00,520 --> 00:27:03,730 I think it's a lecture 34. 487 00:27:03,730 --> 00:27:05,680 So we have a ways to go. 488 00:27:05,680 --> 00:27:06,910 All right. 489 00:27:06,910 --> 00:27:10,000 So let's think about what is true, then, 490 00:27:10,000 --> 00:27:13,540 if delta H0 is less than 0. 491 00:27:13,540 --> 00:27:17,466 First of all, is that exothermic or endothermic? 492 00:27:17,466 --> 00:27:19,021 Exothermic. 493 00:27:19,021 --> 00:27:19,710 All right. 494 00:27:19,710 --> 00:27:21,980 So now we're going to think about increasing 495 00:27:21,980 --> 00:27:24,730 the temperature of an exothermic reaction. 496 00:27:24,730 --> 00:27:28,760 So temperature 2 is going to be greater than temperature 1. 497 00:27:28,760 --> 00:27:31,450 And we already thought about what was going to happen. 498 00:27:31,450 --> 00:27:34,880 But let's make sure this equation is valid and works 499 00:27:34,880 --> 00:27:36,410 for what we just saw. 500 00:27:36,410 --> 00:27:38,370 So if we increase the temperature here, 501 00:27:38,370 --> 00:27:39,980 what's true about this equation? 502 00:27:39,980 --> 00:27:43,490 Well, what's true is you have a minus sign here. 503 00:27:43,490 --> 00:27:46,830 Delta H is negative for exothermic. 504 00:27:46,830 --> 00:27:49,710 And if your temperature 2 is greater than temperature 1, 505 00:27:49,710 --> 00:27:51,260 that's also a negative. 506 00:27:51,260 --> 00:27:54,120 So overall, you're going to have a negative value. 507 00:27:54,120 --> 00:27:56,450 And if you have a negative value here, 508 00:27:56,450 --> 00:28:00,630 that's going to mean that K1 is greater than K2, 509 00:28:00,630 --> 00:28:03,300 which means that, at your new equilibrium, 510 00:28:03,300 --> 00:28:05,461 there'll be fewer products. 511 00:28:05,461 --> 00:28:05,960 All right. 512 00:28:05,960 --> 00:28:09,020 Well, this works with what we were just talking about. 513 00:28:09,020 --> 00:28:13,110 If you increase the temperature of an exothermic reaction, 514 00:28:13,110 --> 00:28:16,430 it shifts it toward reactants to absorb the heat. 515 00:28:16,430 --> 00:28:19,430 So there would be less products. 516 00:28:19,430 --> 00:28:22,050 We've shifted toward reactants. 517 00:28:22,050 --> 00:28:25,970 So you can just think about what's 518 00:28:25,970 --> 00:28:27,680 happening and moving in the direction 519 00:28:27,680 --> 00:28:29,000 to minimize the stress. 520 00:28:29,000 --> 00:28:30,630 And you can also look at the equation 521 00:28:30,630 --> 00:28:32,480 and mathematically figure out what's 522 00:28:32,480 --> 00:28:35,400 going to be true about the equilibrium constants. 523 00:28:35,400 --> 00:28:37,230 It's great to have a backup plan. 524 00:28:37,230 --> 00:28:37,730 All right. 525 00:28:37,730 --> 00:28:39,920 So if we decrease the temperature, 526 00:28:39,920 --> 00:28:42,630 T2 is less than T1. 527 00:28:42,630 --> 00:28:45,230 So now we have our minus. 528 00:28:45,230 --> 00:28:46,010 We have a minus. 529 00:28:46,010 --> 00:28:48,230 But now this is a plus term. 530 00:28:48,230 --> 00:28:52,590 And so that's going to mean our K1 is less than K2. 531 00:28:52,590 --> 00:28:54,360 We have more products here. 532 00:28:54,360 --> 00:28:56,000 So if we decrease the temperature 533 00:28:56,000 --> 00:28:59,990 of an exothermic reaction, the reaction responds in such a way 534 00:28:59,990 --> 00:29:02,550 to minimize the stress, add more heat. 535 00:29:02,550 --> 00:29:06,230 So you switch to the exothermic direction. 536 00:29:06,230 --> 00:29:08,450 And so you should have more products 537 00:29:08,450 --> 00:29:12,110 at this new equilibrium. 538 00:29:12,110 --> 00:29:12,870 All right. 539 00:29:12,870 --> 00:29:14,540 So now, why don't you tell me what 540 00:29:14,540 --> 00:29:16,860 should happen for the scenario where 541 00:29:16,860 --> 00:29:19,320 delta H0 is greater than 0? 542 00:29:19,320 --> 00:29:21,110 Which of the following should be true? 543 00:29:42,152 --> 00:29:43,276 All right, 10 more seconds. 544 00:29:59,490 --> 00:30:03,210 Yeah, so most people are right in that-- yeah. 545 00:30:03,210 --> 00:30:06,030 I think this is a good example of how, 546 00:30:06,030 --> 00:30:08,030 when things are expressed different ways, 547 00:30:08,030 --> 00:30:09,990 sometimes it's hard to see that it all 548 00:30:09,990 --> 00:30:13,060 is consistent with each other. 549 00:30:13,060 --> 00:30:17,900 So yeah, all of those turn out to be true. 550 00:30:17,900 --> 00:30:21,530 All right, so let's look at it over here. 551 00:30:21,530 --> 00:30:24,670 So this is an endothermic reaction. 552 00:30:24,670 --> 00:30:28,740 When we increase the temperature of an endothermic reaction, 553 00:30:28,740 --> 00:30:30,300 you still have this minus sign. 554 00:30:30,300 --> 00:30:32,380 But now this is plus. 555 00:30:32,380 --> 00:30:34,965 But when we've increased the temperature, this is minus. 556 00:30:34,965 --> 00:30:38,040 So you get an overall plus in signs, which 557 00:30:38,040 --> 00:30:41,380 means that K1 is less than K2. 558 00:30:41,380 --> 00:30:45,060 Increasing the temperature of an endothermic reaction 559 00:30:45,060 --> 00:30:47,250 shifts it toward products. 560 00:30:47,250 --> 00:30:51,340 If we decrease the temperature, the net sign is negative here. 561 00:30:51,340 --> 00:30:54,400 So K1 is going to be greater than K2. 562 00:30:54,400 --> 00:30:55,930 We decrease the temperature. 563 00:30:55,930 --> 00:30:59,100 It shifts in the exothermic backwards direction, 564 00:30:59,100 --> 00:31:01,530 and we have less products. 565 00:31:01,530 --> 00:31:03,000 All right. 566 00:31:03,000 --> 00:31:05,620 So K changes with temperature. 567 00:31:05,620 --> 00:31:08,850 You can see this equation on your equation sheet 568 00:31:08,850 --> 00:31:13,570 or just think about minimizing the stress. 569 00:31:13,570 --> 00:31:15,670 So what is this useful for? 570 00:31:15,670 --> 00:31:18,480 Well, figuring out how to maximize 571 00:31:18,480 --> 00:31:22,630 the yield of a reaction can be very important in industry. 572 00:31:22,630 --> 00:31:26,550 One process that is an important industrial process 573 00:31:26,550 --> 00:31:28,690 is the Haber-Bosch process, where 574 00:31:28,690 --> 00:31:33,270 you take nitrogen gas and hydrogen gas and make ammonia. 575 00:31:33,270 --> 00:31:37,930 This process, which was developed a long time ago, 576 00:31:37,930 --> 00:31:39,700 is still used today. 577 00:31:39,700 --> 00:31:43,290 And each year, you make 1.6 times 10 578 00:31:43,290 --> 00:31:45,640 to the 10th kilograms of ammonia, 579 00:31:45,640 --> 00:31:48,160 which you use for fertilizer and other things. 580 00:31:48,160 --> 00:31:50,250 You know what other things ammonia is often 581 00:31:50,250 --> 00:31:53,330 used for besides fertilizer? 582 00:31:53,330 --> 00:31:55,120 Explosives, yeah. 583 00:31:55,120 --> 00:32:00,190 So if you look at the dates of these process development 584 00:32:00,190 --> 00:32:04,530 and the names of these people, they're German. 585 00:32:04,530 --> 00:32:09,030 And so we have World War I and World War II. 586 00:32:09,030 --> 00:32:12,190 I'm thinking that the push to come up with this process 587 00:32:12,190 --> 00:32:17,170 was probably not for fertilizer and the farmers at this time. 588 00:32:17,170 --> 00:32:20,170 This was an important part of the war effort, 589 00:32:20,170 --> 00:32:23,310 to get this process to work to make explosives. 590 00:32:23,310 --> 00:32:27,450 So Haber over here also is considered 591 00:32:27,450 --> 00:32:29,850 the father of chemical weapons. 592 00:32:29,850 --> 00:32:33,030 He came up with gases, such as phosgene. 593 00:32:33,030 --> 00:32:38,080 And he would study the effects of how they killed people. 594 00:32:38,080 --> 00:32:42,540 And one of the ironies is that he was Jewish. 595 00:32:42,540 --> 00:32:46,350 And so a lot of his discoveries were used and resulted 596 00:32:46,350 --> 00:32:49,890 in his relatives dying. 597 00:32:49,890 --> 00:32:55,130 So he was an interesting figure in history. 598 00:32:55,130 --> 00:32:58,620 Carl Bosch, on the other hand, disapproved strongly of Hitler 599 00:32:58,620 --> 00:33:00,690 and was fired from his post. 600 00:33:00,690 --> 00:33:03,780 He didn't lose his life, but his career was ended. 601 00:33:03,780 --> 00:33:08,850 But he still had his Nobel Prize, so maybe it was OK. 602 00:33:08,850 --> 00:33:14,700 So this is an interesting little history about chemistry. 603 00:33:14,700 --> 00:33:16,370 But this process is still used now. 604 00:33:16,370 --> 00:33:19,560 No one has come up with anything better. 605 00:33:19,560 --> 00:33:22,320 And we could think about, what are the challenges 606 00:33:22,320 --> 00:33:25,110 of making this reaction go? 607 00:33:25,110 --> 00:33:28,090 So it's an exothermic reaction. 608 00:33:28,090 --> 00:33:30,600 So what temperature would you want 609 00:33:30,600 --> 00:33:33,860 to use to get more products? 610 00:33:33,860 --> 00:33:36,060 Right, you want to use low temperature, 611 00:33:36,060 --> 00:33:37,920 because that would favor your products. 612 00:33:37,920 --> 00:33:42,570 But low temperature is also sometimes not great, 613 00:33:42,570 --> 00:33:45,340 because it slows the rate, which is bad. 614 00:33:45,340 --> 00:33:48,930 So the compromise temperature that's used in this process 615 00:33:48,930 --> 00:33:51,120 is 500 degrees Celsius. 616 00:33:51,120 --> 00:33:52,470 So it's pretty hot. 617 00:33:52,470 --> 00:33:56,100 So this works, again, maximizing the yield of products. 618 00:33:56,100 --> 00:34:00,900 So what are other ways to drive this toward products? 619 00:34:00,900 --> 00:34:04,900 So can someone suggest another way [INAUDIBLE]? 620 00:34:04,900 --> 00:34:07,362 I don't think I have two [INAUDIBLE]. 621 00:34:07,362 --> 00:34:08,820 If you have your parents here, they 622 00:34:08,820 --> 00:34:11,920 might want this lovely residential water bottle. 623 00:34:11,920 --> 00:34:13,884 [LAUGHTER] 624 00:34:13,884 --> 00:34:17,586 What are other ways to drive this toward products? 625 00:34:17,586 --> 00:34:20,790 Maybe someone could run the mic up there. 626 00:34:34,020 --> 00:34:35,699 Is this-- yeah, it's gone. 627 00:34:35,699 --> 00:34:37,512 You could decrease the volume? 628 00:34:37,512 --> 00:34:38,590 Yep. 629 00:34:38,590 --> 00:34:39,427 Yes! 630 00:34:39,427 --> 00:34:39,927 Yep. 631 00:34:39,927 --> 00:34:40,923 [LAUGHTER AND APPLAUSE] 632 00:34:40,923 --> 00:34:43,110 [CHEERING] 633 00:34:43,110 --> 00:34:47,170 So there's a couple things that you can do. 634 00:34:47,170 --> 00:34:50,580 One is you compress the volume. 635 00:34:50,580 --> 00:34:53,040 And the reason why this works is that, 636 00:34:53,040 --> 00:34:55,739 if you note you have four molecules over here-- 1 637 00:34:55,739 --> 00:34:57,690 plus 3 going to 2. 638 00:34:57,690 --> 00:35:00,780 So if you compress that volume down, 639 00:35:00,780 --> 00:35:04,600 you're going to shift it toward the fewer number of molecules, 640 00:35:04,600 --> 00:35:05,220 which is 2. 641 00:35:05,220 --> 00:35:07,390 So that shifts it toward products. 642 00:35:07,390 --> 00:35:10,230 The other thing that they do is they actually remove products 643 00:35:10,230 --> 00:35:11,530 from the reaction. 644 00:35:11,530 --> 00:35:14,760 So they liquefy out the product at some point. 645 00:35:14,760 --> 00:35:17,040 And when you remove the product, that also 646 00:35:17,040 --> 00:35:19,080 shifts the reaction toward more products 647 00:35:19,080 --> 00:35:20,590 to minimize the stress. 648 00:35:20,590 --> 00:35:22,530 So these are two of the things that are done. 649 00:35:22,530 --> 00:35:25,980 So you have to have high pressure 650 00:35:25,980 --> 00:35:29,250 to compress that volume down and high temperatures. 651 00:35:29,250 --> 00:35:31,870 So this process costs a lot of energy. 652 00:35:31,870 --> 00:35:35,910 So we spend a lot of energy in this country 653 00:35:35,910 --> 00:35:37,470 doing this reaction. 654 00:35:37,470 --> 00:35:40,680 And the reason why is because it's 655 00:35:40,680 --> 00:35:43,670 really hard to split nitrogen. So what kind of bond 656 00:35:43,670 --> 00:35:46,164 does nitrogen have, N2 have? 657 00:35:46,164 --> 00:35:46,955 Triple bond, right. 658 00:35:46,955 --> 00:35:47,859 It's very hard. 659 00:35:47,859 --> 00:35:48,900 It has a high bond order. 660 00:35:48,900 --> 00:35:50,730 It's very hard to break that bond. 661 00:35:50,730 --> 00:35:53,430 And so you really have to work at breaking it. 662 00:35:53,430 --> 00:35:57,300 So if you're doing industry, there's 663 00:35:57,300 --> 00:35:59,190 lots of nitrogen in the air. 664 00:35:59,190 --> 00:36:01,080 So a lot of it is available. 665 00:36:01,080 --> 00:36:04,860 But it's just very hard to utilize it to fix that nitrogen 666 00:36:04,860 --> 00:36:06,420 into another form. 667 00:36:06,420 --> 00:36:09,540 So lots of nitrogen in the air. 668 00:36:09,540 --> 00:36:11,610 Nitrogen is needed by all living things, 669 00:36:11,610 --> 00:36:14,880 but it's really hard to break that triple bond. 670 00:36:14,880 --> 00:36:18,270 But if you're a bacteria, you have a much easier time doing 671 00:36:18,270 --> 00:36:21,000 this than if you are a person. 672 00:36:21,000 --> 00:36:25,320 And bacteria have an enzyme called nitrogenase. 673 00:36:25,320 --> 00:36:27,280 Adding the "-ase" means it's an enzyme. 674 00:36:27,280 --> 00:36:29,850 So this is an enzyme that works on nitrogen. 675 00:36:29,850 --> 00:36:31,470 Most people call it "nit-raw-genase," 676 00:36:31,470 --> 00:36:33,390 but it's really "nitrogen-ace." 677 00:36:33,390 --> 00:36:34,620 And it splits nitrogen. 678 00:36:34,620 --> 00:36:38,760 And it does this by these really complex metallocofactors. 679 00:36:38,760 --> 00:36:40,440 Lots of metals in here. 680 00:36:40,440 --> 00:36:42,150 You have iron and molybdenum. 681 00:36:42,150 --> 00:36:44,190 You also have inorganic sulfur. 682 00:36:44,190 --> 00:36:46,720 And it's those d-orbitals that let you do this. 683 00:36:46,720 --> 00:36:49,560 So you can use high temperatures, high pressure. 684 00:36:49,560 --> 00:36:52,740 Or you can get a transition metal with beautiful d-orbitals 685 00:36:52,740 --> 00:36:54,152 to do your work for you. 686 00:36:54,152 --> 00:36:55,860 And a lot of people are trying to come up 687 00:36:55,860 --> 00:36:59,650 with their own catalyst inspired by nature to get this to work. 688 00:36:59,650 --> 00:37:01,950 So this is an ongoing area of research. 689 00:37:01,950 --> 00:37:04,770 And I just want to mention one of the leaders in the field. 690 00:37:04,770 --> 00:37:07,890 This is a husband-and-wife team, actually. 691 00:37:07,890 --> 00:37:11,460 And Markus Ribbe is a German with a very heavy 692 00:37:11,460 --> 00:37:12,600 German accent. 693 00:37:12,600 --> 00:37:15,840 And so Germans have been dominating this nitrogen fixing 694 00:37:15,840 --> 00:37:17,730 field for a very long time. 695 00:37:17,730 --> 00:37:20,520 But Markus Ribbe is like the nicest person you would ever 696 00:37:20,520 --> 00:37:22,380 meet in your entire life. 697 00:37:22,380 --> 00:37:25,330 And he's trying to figure out environmentally friendly ways 698 00:37:25,330 --> 00:37:25,830 to do it. 699 00:37:25,830 --> 00:37:28,770 So again, chemistry is a powerful tool 700 00:37:28,770 --> 00:37:29,790 to change the world. 701 00:37:29,790 --> 00:37:31,990 But let's change it for the better, please, 702 00:37:31,990 --> 00:37:35,910 and try to come up with ways to protect our environment. 703 00:37:35,910 --> 00:37:38,340 All right, so there's one application 704 00:37:38,340 --> 00:37:41,610 of Le Chatelier's principle, maximizing 705 00:37:41,610 --> 00:37:44,790 the yield of a reaction. 706 00:37:44,790 --> 00:37:49,860 Another example comes in medicine and Le Chatelier's 707 00:37:49,860 --> 00:37:53,340 principle with respect to another metalloprotein, 708 00:37:53,340 --> 00:37:54,300 which is hemoglobin. 709 00:37:54,300 --> 00:37:58,350 So hemoglobin has a "heme," which is iron, more d-orbitals. 710 00:37:58,350 --> 00:38:01,110 If I'm this excited now, wait till I get to d-orbitals. 711 00:38:01,110 --> 00:38:02,430 It's very exciting. 712 00:38:02,430 --> 00:38:03,210 I can't wait. 713 00:38:03,210 --> 00:38:06,210 I love transition metals. 714 00:38:06,210 --> 00:38:08,820 So anyway, so we have hemoglobin. 715 00:38:08,820 --> 00:38:13,570 So hemoglobin Hb plus oxygen yields oxyhemoglobin. 716 00:38:13,570 --> 00:38:15,610 It's hemoglobin with oxygen bound. 717 00:38:15,610 --> 00:38:17,520 And this is an incredibly important reaction, 718 00:38:17,520 --> 00:38:20,960 because otherwise your air, your O2, would be in your lungs 719 00:38:20,960 --> 00:38:22,050 and wouldn't leave. 720 00:38:22,050 --> 00:38:24,020 But hemoglobin carries it to the body, where 721 00:38:24,020 --> 00:38:26,020 it can be used to make energy. 722 00:38:26,020 --> 00:38:27,540 So we really need the reaction. 723 00:38:27,540 --> 00:38:31,278 We want to maximize the product of that reaction. 724 00:38:31,278 --> 00:38:35,980 So this disequilibrium can be shifted 725 00:38:35,980 --> 00:38:41,610 if you have less O2 around, a lower partial pressure of O2. 726 00:38:41,610 --> 00:38:45,910 And this can happen as you go up in altitude. 727 00:38:45,910 --> 00:38:48,980 The pressure of oxygen decreases, 728 00:38:48,980 --> 00:38:50,400 and that's a real problem. 729 00:38:50,400 --> 00:38:53,340 So any of you real serious mountain climbers? 730 00:38:56,000 --> 00:38:56,850 At least one. 731 00:38:56,850 --> 00:38:59,790 How about somewhat serious, climbed 732 00:38:59,790 --> 00:39:01,980 a mountain, maybe worried about your hemoglobin 733 00:39:01,980 --> 00:39:03,780 levels, altitude thickness? 734 00:39:03,780 --> 00:39:04,940 A few, OK. 735 00:39:04,940 --> 00:39:08,400 So what can happen here is, when you have, 736 00:39:08,400 --> 00:39:11,700 again, lower pressure, then the reaction 737 00:39:11,700 --> 00:39:13,660 shifts in the opposite direction. 738 00:39:13,660 --> 00:39:16,770 It's like you have a lower amount of reactant, 739 00:39:16,770 --> 00:39:19,380 so you shift to make more reactant. 740 00:39:19,380 --> 00:39:20,550 And this is what happens. 741 00:39:20,550 --> 00:39:23,700 You have less oxygenated hemoglobin, 742 00:39:23,700 --> 00:39:25,690 and that can make you pretty sick. 743 00:39:25,690 --> 00:39:27,840 So for some of you if you want to say, 744 00:39:27,840 --> 00:39:30,100 what can you do about this? 745 00:39:30,100 --> 00:39:32,320 How can you shift the reaction back the other way? 746 00:39:32,320 --> 00:39:33,653 Do you know what your body does? 747 00:39:33,653 --> 00:39:34,800 Your body is very clever. 748 00:39:34,800 --> 00:39:35,594 What does it do? 749 00:39:39,760 --> 00:39:43,080 Yeah, so it makes it more hemoglobin. 750 00:39:43,080 --> 00:39:45,630 So that's why you need to give your body a little time 751 00:39:45,630 --> 00:39:47,010 to adjust. 752 00:39:47,010 --> 00:39:48,570 Can't do it immediately. 753 00:39:48,570 --> 00:39:51,230 You have to give it a little time to make more protein. 754 00:39:51,230 --> 00:39:56,010 But when you increase the amount of reactant, 755 00:39:56,010 --> 00:39:57,910 it'll shift toward product. 756 00:39:57,910 --> 00:39:59,820 So when you increase the reactants 757 00:39:59,820 --> 00:40:04,770 to minimize the stress, it shifts to make more products. 758 00:40:04,770 --> 00:40:10,860 So this is how the body compensates. 759 00:40:10,860 --> 00:40:15,690 So I'm going to tell you very briefly 760 00:40:15,690 --> 00:40:18,450 about significant figures, and then I'm 761 00:40:18,450 --> 00:40:22,400 going to have time to show you a Mole Day video. 762 00:40:22,400 --> 00:40:24,450 And it's actually from UC Irvine, 763 00:40:24,450 --> 00:40:26,130 where Markus Ribbe is from. 764 00:40:26,130 --> 00:40:29,460 So today, we're celebrating UC Irvine chemistry department. 765 00:40:29,460 --> 00:40:33,090 Anyway, I just want to mention significant figures. 766 00:40:33,090 --> 00:40:34,750 I have a confession to make. 767 00:40:34,750 --> 00:40:37,080 I didn't know the rules of significant figures 768 00:40:37,080 --> 00:40:39,890 for logs when I started teaching this course. 769 00:40:39,890 --> 00:40:41,370 And this will be information that I 770 00:40:41,370 --> 00:40:46,680 think now I'll have to purge from my brain on my deathbed. 771 00:40:46,680 --> 00:40:49,860 But pay attention to these, and we'll 772 00:40:49,860 --> 00:40:51,370 have some clicker questions on them. 773 00:40:51,370 --> 00:40:52,300 So that'll be fun. 774 00:40:52,300 --> 00:40:52,800 OK. 775 00:40:52,800 --> 00:40:58,870 So let's look at these two-- log of two different numbers. 776 00:40:58,870 --> 00:41:02,730 Note the 3 here is the 3 over here. 777 00:41:02,730 --> 00:41:09,510 The 23, 10 to the 23-- 10 to the 23, Mole Day-- is the 23 here. 778 00:41:09,510 --> 00:41:11,400 But those are not significant. 779 00:41:11,400 --> 00:41:14,940 That 3 and that 23 are not significant figures. 780 00:41:14,940 --> 00:41:18,900 These are the significant figures-- 7.310. 781 00:41:18,900 --> 00:41:22,320 So there are four significant figures here. 782 00:41:22,320 --> 00:41:27,730 Those four significant figures end up after the decimal point. 783 00:41:27,730 --> 00:41:29,940 So those are the significant figures 784 00:41:29,940 --> 00:41:32,020 after the decimal point. 785 00:41:32,020 --> 00:41:36,090 And if you go the other direction, if you have a 0.389 786 00:41:36,090 --> 00:41:39,670 here, that has three significant figures. 787 00:41:39,670 --> 00:41:41,790 So three significant figures here. 788 00:41:41,790 --> 00:41:45,420 But if you have 12.389, you still 789 00:41:45,420 --> 00:41:48,660 have three significant figures, because that 12 ends up 790 00:41:48,660 --> 00:41:50,070 over here. 791 00:41:50,070 --> 00:41:51,150 All right. 792 00:41:51,150 --> 00:41:54,468 With that, give it a try. 793 00:41:58,890 --> 00:42:02,240 This could be for the clicker championship of today. 794 00:42:17,940 --> 00:42:18,510 All right. 795 00:42:18,510 --> 00:42:20,060 Let's just do 10 more seconds. 796 00:42:33,650 --> 00:42:35,450 Should I show my video first, or do you 797 00:42:35,450 --> 00:42:36,650 want to do the winner first? 798 00:42:36,650 --> 00:42:37,820 Do winner first. 799 00:42:37,820 --> 00:42:39,650 Winner first, OK. 800 00:42:39,650 --> 00:42:41,480 All right. 801 00:42:41,480 --> 00:42:45,767 OK, so 3 after the decimal place. 802 00:42:45,767 --> 00:42:47,600 And let's look at the winner, and then we're 803 00:42:47,600 --> 00:42:51,245 going to end with a short video. 804 00:42:51,245 --> 00:42:53,750 Oh, man! 805 00:42:53,750 --> 00:42:55,200 All right. 806 00:42:55,200 --> 00:42:57,446 Dan, whoa. 807 00:42:57,446 --> 00:42:57,945 OK. 808 00:43:00,500 --> 00:43:03,890 All right, so we're going to end with a short video. 809 00:43:03,890 --> 00:43:06,060 And here it is. 810 00:43:06,060 --> 00:43:08,485 [VIDEO PLAYBACK] 811 00:43:08,485 --> 00:43:12,365 [MUSIC - "LET IT GO"] 812 00:43:20,130 --> 00:43:23,409 - (SINGING) Snow looks white, 'cause it's scattering light 813 00:43:23,409 --> 00:43:23,908 elastically. 814 00:43:27,180 --> 00:43:31,313 Atoms are everywhere I look, though none of them 815 00:43:31,313 --> 00:43:33,870 can be seen. 816 00:43:33,870 --> 00:43:41,400 Molecules have always been a challenge to resolve. 817 00:43:41,400 --> 00:43:43,370 Light microscopes don't work. 818 00:43:43,370 --> 00:43:45,142 Heavens knows we tried. 819 00:43:48,058 --> 00:43:50,220 Do they exist? 820 00:43:50,220 --> 00:43:51,663 Can they been seen? 821 00:43:51,663 --> 00:43:55,090 Maybe using some spectroscopy! 822 00:43:55,090 --> 00:44:01,190 For centuries, we didn't know. 823 00:44:01,190 --> 00:44:04,636 Well, now we know! 824 00:44:04,636 --> 00:44:08,880 Chemists know, chemists know what 825 00:44:08,880 --> 00:44:11,675 makes water freeze and flow. 826 00:44:11,675 --> 00:44:18,980 Chemists know, chemists know why fireflies can glow. 827 00:44:18,980 --> 00:44:29,330 All chemists know Avogadro order 10 to 23. 828 00:44:29,330 --> 00:44:31,884 The moles never bothered me anyway. 829 00:44:37,050 --> 00:44:43,640 Angstroms measure distance, nomenclature hard to say. 830 00:44:43,640 --> 00:44:50,820 Though we are macroscopic, we always find a way! 831 00:44:50,820 --> 00:44:55,628 We love to see what we can do, synthesizing 832 00:44:55,628 --> 00:45:02,487 novel molecules from Exclusion Principle of Pauli-- chemistry! 833 00:45:05,409 --> 00:45:12,714 Chemists know, chemists know about ozone in the sky. 834 00:45:12,714 --> 00:45:19,600 Chemists know, chemists know sigma bonding versus pi. 835 00:45:19,600 --> 00:45:26,488 We understand Le Chatelier. 836 00:45:26,488 --> 00:45:26,988 Equilibrium! 837 00:45:37,670 --> 00:45:41,526 There's chemistry to be found from the air down 838 00:45:41,526 --> 00:45:44,418 to the ground. 839 00:45:44,418 --> 00:45:48,360 We make these compounds form in flasks 840 00:45:48,360 --> 00:45:51,839 with bottoms that are round. 841 00:45:51,839 --> 00:45:58,545 We hope they crystallize, 'cause columns are the worst. 842 00:45:58,545 --> 00:46:06,230 Still we strive to do all this for the chance to be the first! 843 00:46:06,230 --> 00:46:13,136 Chemists know, chemists know why it's red at the break of dawn. 844 00:46:13,136 --> 00:46:17,600 Chemists know, chemists know where 845 00:46:17,600 --> 00:46:20,576 reactants go when they're gone. 846 00:46:20,576 --> 00:46:31,488 We need to know every single way to form or break bonds! 847 00:46:34,500 --> 00:46:38,140 The moles never bothered me anyway. 848 00:46:38,140 --> 00:46:39,610 [END PLAYBACK] 849 00:46:39,610 --> 00:46:43,040 [APPLAUSE] 850 00:46:43,040 --> 00:46:45,230 All right, have a great weekend. 851 00:46:45,230 --> 00:46:48,910 Please return any borrowed clickers.