1 00:00:00,000 --> 00:00:07,207 [MUSIC PLAYING] 2 00:00:07,207 --> 00:00:08,540 JESSICA HARROP: Hi, I'm Jessica. 3 00:00:08,540 --> 00:00:09,914 And today I'm going to be talking 4 00:00:09,914 --> 00:00:16,280 about a chemical demonstration I like to call the steaming gun. 5 00:00:16,280 --> 00:00:19,640 So you've probably seen this before at the drugstore 6 00:00:19,640 --> 00:00:20,930 or in your house. 7 00:00:20,930 --> 00:00:23,060 It's called hydrogen peroxide and it's 8 00:00:23,060 --> 00:00:25,280 the stuff you put on cuts. 9 00:00:25,280 --> 00:00:27,320 But it has many other uses as well, 10 00:00:27,320 --> 00:00:29,930 from bleaching things to powering rockets, 11 00:00:29,930 --> 00:00:31,760 depending on its concentration. 12 00:00:31,760 --> 00:00:36,110 The solution that you get at the drugstore is usually 3%. 13 00:00:36,110 --> 00:00:42,080 So it's called hydrogen peroxide and it's chemical formula 14 00:00:42,080 --> 00:00:45,200 is H2O2. 15 00:00:45,200 --> 00:00:47,620 So the atoms are arranged like this. 16 00:00:50,170 --> 00:00:52,840 It sort of looks like water, but the extra oxygen 17 00:00:52,840 --> 00:00:55,720 makes the molecule more reactive. 18 00:00:55,720 --> 00:00:58,060 Now if you leave it alone, it decomposes 19 00:00:58,060 --> 00:01:01,340 into water and oxygen. The equation looks like this. 20 00:01:03,998 --> 00:01:08,130 I'm going to balance it. 21 00:01:08,130 --> 00:01:09,930 Now, normally, you can't see this reaction 22 00:01:09,930 --> 00:01:12,990 happening because at room temperature, it's very slow. 23 00:01:12,990 --> 00:01:14,940 But there are many ways to speed it up 24 00:01:14,940 --> 00:01:18,120 like increasing the temperature or adding a catalyst. 25 00:01:18,120 --> 00:01:21,210 In this demonstration MIT's Dr. Dolhun 26 00:01:21,210 --> 00:01:24,180 uses a catalyst to make the reaction go thousands 27 00:01:24,180 --> 00:01:26,070 of times faster than normal. 28 00:01:26,070 --> 00:01:27,300 Let's watch. 29 00:01:27,300 --> 00:01:30,810 JOHN DOLHUN: So we're going to do this experiment here. 30 00:01:30,810 --> 00:01:35,330 And basically what we've got is we've got four bottles. 31 00:01:35,330 --> 00:01:37,890 We're each going to do the experiment in a bottle. 32 00:01:37,890 --> 00:01:42,450 We've got 15 mLs of hydrogen peroxide here. 33 00:01:42,450 --> 00:01:47,460 And we're going to be using a man-made catalyst. 34 00:01:47,460 --> 00:01:49,345 We're going to be using manganese dioxide. 35 00:01:55,620 --> 00:01:57,975 And we're each going to take a scoop of this. 36 00:02:08,991 --> 00:02:10,199 And we're going to put it in. 37 00:02:16,260 --> 00:02:17,690 You can set it down on the tray. 38 00:02:20,370 --> 00:02:23,550 And just-- it's starting to work. 39 00:02:23,550 --> 00:02:26,880 You won't have to stand up to see this. 40 00:02:26,880 --> 00:02:30,480 You can start to see some condensed water vapor forming 41 00:02:30,480 --> 00:02:31,650 inside the flasks. 42 00:02:31,650 --> 00:02:36,060 Oxygen bundles are coming out. 43 00:02:36,060 --> 00:02:38,370 Now we're just going to lightly hold that. 44 00:02:38,370 --> 00:02:38,870 Whew! 45 00:02:45,530 --> 00:02:47,170 JESSICA HARROP: OK, so what happened? 46 00:02:47,170 --> 00:02:50,950 Dr. Dolhun had hydrogen peroxide in the plastic bottle. 47 00:02:50,950 --> 00:02:57,990 Then he added a catalyst, some manganese dioxide or MNO2, 48 00:02:57,990 --> 00:03:01,150 and got a plume of water vapor. 49 00:03:01,150 --> 00:03:03,450 So let's talk about how a catalyst works. 50 00:03:03,450 --> 00:03:05,070 I'm going to draw a potential energy 51 00:03:05,070 --> 00:03:07,114 diagram for this reaction. 52 00:03:07,114 --> 00:03:20,690 [MUSIC PLAYING] 53 00:03:20,690 --> 00:03:23,260 So here's my potential energy diagram. 54 00:03:23,260 --> 00:03:25,510 So I've got potential energy on the y-axis 55 00:03:25,510 --> 00:03:29,620 and the reaction coordinate, or time, on the x-axis. 56 00:03:29,620 --> 00:03:32,020 The reactants are starting at this amount of energy 57 00:03:32,020 --> 00:03:34,680 and the products have this amount. 58 00:03:34,680 --> 00:03:37,270 Here, EA, that's the activation energy. 59 00:03:37,270 --> 00:03:40,450 It's the amount of energy you need to add to the reactants 60 00:03:40,450 --> 00:03:42,420 to make the reaction go. 61 00:03:42,420 --> 00:03:45,430 And delta H, that's the amount of energy that's released 62 00:03:45,430 --> 00:03:46,870 when the reaction happens. 63 00:03:46,870 --> 00:03:49,460 Now let's see what happens when I add a catalyst. 64 00:03:49,460 --> 00:03:56,400 [MUSIC PLAYING] 65 00:03:56,400 --> 00:04:00,270 With a catalyst, my activation energy is a lot lower. 66 00:04:00,270 --> 00:04:02,610 And even a small reduction in activation energy 67 00:04:02,610 --> 00:04:05,220 can make the reaction go thousands of times faster 68 00:04:05,220 --> 00:04:06,460 than it normally would. 69 00:04:06,460 --> 00:04:08,460 But notice that regardless of whether or not you 70 00:04:08,460 --> 00:04:11,640 have a catalyst, the delta H, the amount of energy released 71 00:04:11,640 --> 00:04:13,870 in the reaction, doesn't change. 72 00:04:13,870 --> 00:04:16,120 So the catalyst only speeds up the reaction. 73 00:04:16,120 --> 00:04:18,450 It doesn't change the amount of energy released. 74 00:04:18,450 --> 00:04:19,680 Now, take a look at this. 75 00:04:19,680 --> 00:04:21,750 JOHN DOLHUN: Notice the size of the bottles. 76 00:04:21,750 --> 00:04:24,870 These are very exothermic reactions. 77 00:04:24,870 --> 00:04:28,650 The bundles have basically shrunk down 78 00:04:28,650 --> 00:04:32,310 to a very, very tiny size compared 79 00:04:32,310 --> 00:04:33,474 to the control bundles. 80 00:04:33,474 --> 00:04:34,890 JESSICA HARROP: So as you can see, 81 00:04:34,890 --> 00:04:37,530 the catalyzed reaction releases so much heat 82 00:04:37,530 --> 00:04:41,190 that it actually melts the bottles and makes them smaller. 83 00:04:41,190 --> 00:04:43,050 Also, the catalyst itself remains 84 00:04:43,050 --> 00:04:45,090 unchanged by the reaction. 85 00:04:45,090 --> 00:04:46,980 And designing catalysts is actually 86 00:04:46,980 --> 00:04:49,260 a key subfield of chemistry. 87 00:04:49,260 --> 00:04:51,780 MIT's Richard Schrock won the Nobel Prize 88 00:04:51,780 --> 00:04:53,590 working in this field. 89 00:04:53,590 --> 00:04:56,770 And remember how we used H2O2 on our cuts? 90 00:04:56,770 --> 00:04:59,160 Well, we have an enzyme in our bodies called 91 00:04:59,160 --> 00:05:02,790 catalase that does the same thing as the manganese dioxide 92 00:05:02,790 --> 00:05:04,530 that Dr. Dolhun used. 93 00:05:04,530 --> 00:05:07,680 That's why when you put hydrogen peroxide on a cut 94 00:05:07,680 --> 00:05:09,540 you see fizzing and bundles. 95 00:05:09,540 --> 00:05:11,790 The catalase in your blood is breaking down 96 00:05:11,790 --> 00:05:13,410 the hydrogen peroxide. 97 00:05:13,410 --> 00:05:16,560 And according to recent studies, low levels of catalase 98 00:05:16,560 --> 00:05:20,190 may play a role in the graying process of human hair. 99 00:05:20,190 --> 00:05:23,160 If catalase levels are low, it can't break down 100 00:05:23,160 --> 00:05:25,800 all of the hydrogen peroxide in the blood. 101 00:05:25,800 --> 00:05:28,950 And that extra H2O2 starts to bleach your hair 102 00:05:28,950 --> 00:05:30,880 from the inside out. 103 00:05:30,880 --> 00:05:33,180 So to wrap up, catalysts don't change 104 00:05:33,180 --> 00:05:36,090 the products of the reaction or how much 105 00:05:36,090 --> 00:05:38,460 heat is released or absorbed. 106 00:05:38,460 --> 00:05:41,340 They only change the time it takes for the reaction 107 00:05:41,340 --> 00:05:42,045 to finish. 108 00:05:42,045 --> 00:05:42,670 [MUSIC PLAYING] 109 00:05:42,670 --> 00:05:44,086 All right, that's it for me today. 110 00:05:44,086 --> 00:05:45,980 I'll see you next time.