1 00:00:00,000 --> 00:00:00,510 2 00:00:00,510 --> 00:00:03,440 I think we're all reasonably familiar with the three states 3 00:00:03,439 --> 00:00:05,400 of matter in our everyday world. 4 00:00:05,400 --> 00:00:07,679 At very high temperatures you get a fourth. 5 00:00:07,679 --> 00:00:10,990 But the three ones that we normally deal with are, things 6 00:00:10,990 --> 00:00:22,920 could be a solid, a liquid, or it could be a gas. 7 00:00:22,920 --> 00:00:25,960 And we have this general notion, and I think water is 8 00:00:25,960 --> 00:00:29,050 the example that always comes to at least my mind. 9 00:00:29,050 --> 00:00:30,740 Is that solid happens when things are 10 00:00:30,739 --> 00:00:33,719 colder, relatively colder. 11 00:00:33,719 --> 00:00:37,539 And then as you warm up, you go into a liquid state. 12 00:00:37,539 --> 00:00:40,390 And as your warm up even more you go into a gaseous state. 13 00:00:40,390 --> 00:00:44,480 So you go from colder to hotter. 14 00:00:44,479 --> 00:00:51,359 And in the case of water, when you're a solid, you're ice. 15 00:00:51,359 --> 00:00:55,490 When you're a liquid, some people would call ice water, 16 00:00:55,490 --> 00:00:58,490 but let's call it liquid water. 17 00:00:58,490 --> 00:01:01,370 I think we know what that is. 18 00:01:01,369 --> 00:01:04,909 And then when it's in the gas state, you're essentially 19 00:01:04,909 --> 00:01:06,159 vapor or steam. 20 00:01:06,159 --> 00:01:12,569 21 00:01:12,569 --> 00:01:14,809 So let's think a little bit about what, at least in the 22 00:01:14,810 --> 00:01:17,500 case of water, and the analogy will extend to 23 00:01:17,500 --> 00:01:19,040 other types of molecules. 24 00:01:19,040 --> 00:01:22,180 But what is it about water that makes it solid, and when 25 00:01:22,180 --> 00:01:24,600 it's colder, what allows it to be liquid. 26 00:01:24,599 --> 00:01:28,569 And I'll be frank, liquids are kind of fascinating because 27 00:01:28,569 --> 00:01:31,939 you can never nail them down, I guess is the 28 00:01:31,939 --> 00:01:32,890 best way to view them. 29 00:01:32,890 --> 00:01:34,400 Or a gas. 30 00:01:34,400 --> 00:01:36,670 So let's just draw a water molecule. 31 00:01:36,670 --> 00:01:39,939 32 00:01:39,939 --> 00:01:42,750 So you have oxygen there. 33 00:01:42,750 --> 00:01:47,019 You have some bonds to hydrogen. 34 00:01:47,019 --> 00:01:50,369 And then you have two extra pairs of valence electrons in 35 00:01:50,370 --> 00:01:51,320 the oxygen. 36 00:01:51,319 --> 00:01:55,289 And a couple of videos ago, we said oxygen is a lot more 37 00:01:55,290 --> 00:01:58,060 electronegative than the hydrogen. 38 00:01:58,060 --> 00:02:00,329 It likes to hog the electrons. 39 00:02:00,329 --> 00:02:04,429 So even though this shows that they're sharing 40 00:02:04,430 --> 00:02:06,300 electrons here and here. 41 00:02:06,299 --> 00:02:08,840 At both sides of those lines, you can kind of view that 42 00:02:08,840 --> 00:02:10,719 hydrogen is contributing an electron and oxygen is 43 00:02:10,719 --> 00:02:13,020 contributing an electron on both sides of that line. 44 00:02:13,020 --> 00:02:15,650 But we know because of the electronegativity, or the 45 00:02:15,650 --> 00:02:18,700 relative electronegativity of oxygen, that it's hogging 46 00:02:18,699 --> 00:02:19,750 these electrons. 47 00:02:19,750 --> 00:02:22,310 And so the electrons spend a lot more time around the 48 00:02:22,310 --> 00:02:24,610 oxygen than they do around the hydrogen. 49 00:02:24,610 --> 00:02:27,880 And what that results is that on the oxygen side of the 50 00:02:27,879 --> 00:02:32,189 molecule, you end up with a partial negative charge. 51 00:02:32,189 --> 00:02:33,539 And we talked about that a little bit. 52 00:02:33,539 --> 00:02:35,879 And on the hydrogen side of the molecules, you end up with 53 00:02:35,879 --> 00:02:37,474 a slightly positive charge. 54 00:02:37,474 --> 00:02:44,329 55 00:02:44,330 --> 00:02:51,460 Now, if these molecules have very little kinetic energy, 56 00:02:51,460 --> 00:02:56,860 they're not moving around a whole lot, then the positive 57 00:02:56,860 --> 00:02:59,910 sides of the hydrogens are very attracted to the negative 58 00:02:59,909 --> 00:03:03,430 sides of oxygen in other molecules. 59 00:03:03,430 --> 00:03:04,969 Let me draw some more molecules. 60 00:03:04,969 --> 00:03:06,979 When we talk about the whole state of the whole matter, we 61 00:03:06,979 --> 00:03:10,079 actually think about how the molecules are interacting with 62 00:03:10,080 --> 00:03:10,480 each other. 63 00:03:10,479 --> 00:03:13,119 Not just how the atoms are interacting with each other 64 00:03:13,120 --> 00:03:16,050 within a molecule. 65 00:03:16,050 --> 00:03:20,490 I just drew one oxygen, let me copy and paste that. 66 00:03:20,490 --> 00:03:22,390 But I could do multiple oxygens. 67 00:03:22,389 --> 00:03:26,819 And let's say that that hydrogen is going to want to 68 00:03:26,819 --> 00:03:28,310 be near this oxygen. 69 00:03:28,310 --> 00:03:30,409 Because this has partial negative charge, this has a 70 00:03:30,409 --> 00:03:32,669 partial positive charge. 71 00:03:32,669 --> 00:03:37,189 And then I could do another one right there. 72 00:03:37,189 --> 00:03:40,930 And then maybe we'll have, and just to make the point clear, 73 00:03:40,930 --> 00:03:43,110 you have two hydrogens here, maybe an oxygen 74 00:03:43,110 --> 00:03:45,500 wants to hang out there. 75 00:03:45,500 --> 00:03:49,409 So maybe you have an oxygen that wants to be here because 76 00:03:49,409 --> 00:03:52,710 it's got its partial negative here. 77 00:03:52,710 --> 00:03:55,969 And it's connected to two hydrogens right there that 78 00:03:55,969 --> 00:03:57,590 have their partial positives. 79 00:03:57,590 --> 00:04:00,990 But you can kind of see a lattice structure. 80 00:04:00,990 --> 00:04:05,510 Let me draw these bonds, these polar bonds that start forming 81 00:04:05,509 --> 00:04:08,419 between the particles. 82 00:04:08,419 --> 00:04:10,619 These bonds, they're called polar bonds because the 83 00:04:10,620 --> 00:04:14,000 molecules themselves are polar. 84 00:04:14,000 --> 00:04:16,459 And you can see it forms this lattice structure. 85 00:04:16,459 --> 00:04:19,649 And if each of these molecules don't have a 86 00:04:19,649 --> 00:04:21,009 lot of kinetic energy. 87 00:04:21,009 --> 00:04:26,589 Or we could say the average kinetic energy of this matter 88 00:04:26,589 --> 00:04:27,500 is fairly low. 89 00:04:27,500 --> 00:04:29,040 And what do we know is average kinetic energy? 90 00:04:29,040 --> 00:04:30,520 Well, that's temperature. 91 00:04:30,519 --> 00:04:33,839 Then this lattice structure will be solid. 92 00:04:33,839 --> 00:04:37,799 These molecules will not move relative to each other. 93 00:04:37,800 --> 00:04:40,069 I could draw a gazillion more, but I think you get the point 94 00:04:40,069 --> 00:04:44,480 that we're forming this kind of fixed structure. 95 00:04:44,480 --> 00:04:48,100 And while we're in the solid state, as we add kinetic 96 00:04:48,100 --> 00:04:52,040 energy, as we add heat, what it does to molecules is, it 97 00:04:52,040 --> 00:04:53,860 just makes them vibrate around a little bit. 98 00:04:53,860 --> 00:04:57,210 99 00:04:57,209 --> 00:04:59,966 If I was a cartoonist, they way you'd draw a vibration is 100 00:04:59,966 --> 00:05:01,319 to put quotation marks there. 101 00:05:01,319 --> 00:05:03,189 That's not very scientific. 102 00:05:03,189 --> 00:05:05,699 But they would vibrate around, they would buzz around a 103 00:05:05,699 --> 00:05:06,300 little bit. 104 00:05:06,300 --> 00:05:08,579 I'm drawing arrows to show that they are vibrating. 105 00:05:08,579 --> 00:05:09,300 It doesn't have to be just 106 00:05:09,300 --> 00:05:10,810 left-right it could be up-down. 107 00:05:10,810 --> 00:05:14,170 But as you add more and more heat in a solid, these 108 00:05:14,170 --> 00:05:16,650 molecules are going to keep their structure. 109 00:05:16,649 --> 00:05:19,639 So they're not going to move around relative to each other. 110 00:05:19,639 --> 00:05:23,209 But they will convert that heat, and heat is just a form 111 00:05:23,209 --> 00:05:27,129 of energy, into kinetic energy which is expressed as the 112 00:05:27,129 --> 00:05:29,339 vibration of these molecules. 113 00:05:29,339 --> 00:05:33,019 Now, if you make these molecules start to vibrate 114 00:05:33,019 --> 00:05:35,560 enough, and if you put enough kinetic energy into these 115 00:05:35,560 --> 00:05:37,449 molecules, what do you think is going to happen? 116 00:05:37,449 --> 00:05:39,829 Well this guy is vibrating pretty hard, and he's 117 00:05:39,829 --> 00:05:42,339 vibrating harder and harder as you add more and more heat. 118 00:05:42,339 --> 00:05:43,669 This guy is doing the same thing. 119 00:05:43,670 --> 00:05:46,910 At some point, these polar bonds that they have to each 120 00:05:46,910 --> 00:05:50,800 other are going to start not being strong enough to contain 121 00:05:50,800 --> 00:05:52,780 the vibrations. 122 00:05:52,779 --> 00:05:57,039 And once that happens, the molecules-- let me draw a 123 00:05:57,040 --> 00:05:58,879 couple more. 124 00:05:58,879 --> 00:06:01,569 Once that happens, the molecules are going to start 125 00:06:01,569 --> 00:06:02,969 moving past each other. 126 00:06:02,970 --> 00:06:07,970 127 00:06:07,970 --> 00:06:10,765 So now all of a sudden, the molecule will start shifting. 128 00:06:10,764 --> 00:06:13,669 129 00:06:13,670 --> 00:06:14,970 But they're still attracted. 130 00:06:14,970 --> 00:06:17,140 Maybe this side is moving here, that's moving there. 131 00:06:17,139 --> 00:06:19,539 You have other molecules moving around that way. 132 00:06:19,540 --> 00:06:22,120 But they're still attracted to each other. 133 00:06:22,120 --> 00:06:25,449 Even though we've gotten the kinetic energy to the point 134 00:06:25,449 --> 00:06:31,319 that the vibrations can kind of break the bonds between the 135 00:06:31,319 --> 00:06:34,480 polar sides of the molecules. 136 00:06:34,480 --> 00:06:38,259 Our vibration, or our kinetic energy for each molecule, 137 00:06:38,259 --> 00:06:40,550 still isn't strong enough to completely separate them. 138 00:06:40,550 --> 00:06:43,000 They're starting to slide past each other. 139 00:06:43,000 --> 00:06:44,839 And this is essentially what happens when you're in a 140 00:06:44,839 --> 00:06:46,259 liquid state. 141 00:06:46,259 --> 00:06:49,759 You have a lot of atoms that want be touching each other 142 00:06:49,759 --> 00:06:50,750 but they're sliding. 143 00:06:50,750 --> 00:06:53,050 They have enough kinetic energy to slide past each 144 00:06:53,050 --> 00:06:57,480 other and break that solid lattice structure here. 145 00:06:57,480 --> 00:07:00,270 And then if you add even more kinetic energy, even more 146 00:07:00,269 --> 00:07:05,289 heat, at this point it's a solution now. 147 00:07:05,290 --> 00:07:07,010 They're not even going to be able to stay together. 148 00:07:07,009 --> 00:07:08,969 They're not going to be able to stay near each other. 149 00:07:08,970 --> 00:07:11,260 If you add enough kinetic energy they're going to start 150 00:07:11,259 --> 00:07:12,079 looking like this. 151 00:07:12,079 --> 00:07:15,129 They're going to completely separate and then kind of 152 00:07:15,129 --> 00:07:17,329 bounce around independently. 153 00:07:17,329 --> 00:07:19,209 Especially independently if they're an ideal gas. 154 00:07:19,209 --> 00:07:22,560 But in general, in gases, they're no longer touching 155 00:07:22,560 --> 00:07:22,980 each other. 156 00:07:22,980 --> 00:07:25,150 They might bump into each other. 157 00:07:25,149 --> 00:07:28,060 But they have so much kinetic energy on their own that 158 00:07:28,060 --> 00:07:29,430 they're all doing their own thing 159 00:07:29,430 --> 00:07:31,300 and they're not touching. 160 00:07:31,300 --> 00:07:33,650 I think that makes intuitive sense if you just think about 161 00:07:33,649 --> 00:07:36,069 what a gas is. 162 00:07:36,069 --> 00:07:37,699 For example, it's hard to see a gas. 163 00:07:37,699 --> 00:07:39,420 Why is it hard to see a gas? 164 00:07:39,420 --> 00:07:41,660 Because the molecules are much further apart. 165 00:07:41,660 --> 00:07:46,670 So they're not acting on the light in the way that a liquid 166 00:07:46,670 --> 00:07:47,310 or a solid would. 167 00:07:47,310 --> 00:07:50,389 And if we keep making that extended further, a solid-- 168 00:07:50,389 --> 00:07:53,009 well, I probably shouldn't use the example with ice. 169 00:07:53,009 --> 00:07:56,800 Because ice or water is one of the few situations where the 170 00:07:56,800 --> 00:07:58,960 solid is less dense than the liquid. 171 00:07:58,959 --> 00:08:00,439 That's why ice floats. 172 00:08:00,439 --> 00:08:02,959 And that's why icebergs don't just all fall to the 173 00:08:02,959 --> 00:08:03,709 bottom of the ocean. 174 00:08:03,709 --> 00:08:07,089 And ponds don't completely freeze solid. 175 00:08:07,089 --> 00:08:11,869 But you can imagine that, because a liquid is in most 176 00:08:11,870 --> 00:08:13,379 cases other than water, less dense. 177 00:08:13,379 --> 00:08:15,129 That's another reason why you can see through it a little 178 00:08:15,129 --> 00:08:15,829 bit better. 179 00:08:15,829 --> 00:08:18,939 Or it's not diffracting-- well I won't go into that too much, 180 00:08:18,939 --> 00:08:20,040 than maybe even a solid. 181 00:08:20,040 --> 00:08:21,950 But the gas is the most obvious. 182 00:08:21,949 --> 00:08:23,920 And it is true with water. 183 00:08:23,920 --> 00:08:27,699 The liquid form is definitely more dense than the gas form. 184 00:08:27,699 --> 00:08:31,829 In the gas form, the molecules are going to jump around, not 185 00:08:31,829 --> 00:08:32,829 touch each other. 186 00:08:32,830 --> 00:08:35,129 And because of that, more light can 187 00:08:35,129 --> 00:08:37,029 get through the substance. 188 00:08:37,029 --> 00:08:40,308 Now the question is, how do we measure the amount of heat 189 00:08:40,308 --> 00:08:44,939 that it takes to do this to water? 190 00:08:44,940 --> 00:08:47,800 And to explain that, I'll actually draw a 191 00:08:47,799 --> 00:08:49,990 phase change diagram. 192 00:08:49,990 --> 00:08:53,669 Which is a fancy way of describing something fairly 193 00:08:53,669 --> 00:08:54,709 straightforward. 194 00:08:54,710 --> 00:08:57,400 Let me say that this is the amount of heat I'm adding. 195 00:08:57,399 --> 00:08:59,000 And this is the temperature. 196 00:08:59,000 --> 00:09:02,389 We'll talk about the states of matter in a second. 197 00:09:02,389 --> 00:09:06,490 So heat is often denoted by q. 198 00:09:06,490 --> 00:09:09,080 Sometimes people will talk about change in heat. 199 00:09:09,080 --> 00:09:11,680 They'll use H, lowercase and uppercase H. 200 00:09:11,679 --> 00:09:13,449 They'll put a delta in front of the H. 201 00:09:13,450 --> 00:09:15,430 Delta just means change in. 202 00:09:15,429 --> 00:09:17,979 And sometimes you'll hear the word enthalpy. 203 00:09:17,980 --> 00:09:18,740 Let me write that. 204 00:09:18,740 --> 00:09:23,250 Because I used to say what is enthalpy? 205 00:09:23,250 --> 00:09:26,289 206 00:09:26,289 --> 00:09:29,049 It sounds like empathy, but it's 207 00:09:29,049 --> 00:09:30,599 quite a different concept. 208 00:09:30,600 --> 00:09:33,279 At least, as far as my neural connections could make it. 209 00:09:33,279 --> 00:09:36,809 But enthalpy is closely related to heat. 210 00:09:36,809 --> 00:09:38,059 It's heat content. 211 00:09:38,059 --> 00:09:45,889 212 00:09:45,889 --> 00:09:49,250 For our purposes, when you hear someone say change in 213 00:09:49,250 --> 00:09:51,549 enthalpy, you should really just be thinking 214 00:09:51,549 --> 00:09:52,689 of change in heat. 215 00:09:52,690 --> 00:09:56,850 I think this word was really just introduced to confuse 216 00:09:56,850 --> 00:10:00,860 chemistry students and introduce a non-intuitive word 217 00:10:00,860 --> 00:10:02,080 into their vocabulary. 218 00:10:02,080 --> 00:10:04,100 The best way to think about it is heat content. 219 00:10:04,100 --> 00:10:07,129 Change in enthalpy is really just change in heat. 220 00:10:07,129 --> 00:10:09,230 And just remember, all of these things, whether we're 221 00:10:09,230 --> 00:10:13,000 talking about heat, kinetic energy, 222 00:10:13,000 --> 00:10:16,409 potential energy, enthalpy. 223 00:10:16,409 --> 00:10:18,589 You'll hear them in different contexts, and you're like, I 224 00:10:18,590 --> 00:10:19,550 thought I should be using heat and they're 225 00:10:19,549 --> 00:10:21,029 talking about enthalpy. 226 00:10:21,029 --> 00:10:23,299 These are all forms of energy. 227 00:10:23,299 --> 00:10:26,039 And these are all measured in joules. 228 00:10:26,039 --> 00:10:28,099 And they might be measured in other ways, but the 229 00:10:28,100 --> 00:10:29,550 traditional way is in joules. 230 00:10:29,549 --> 00:10:31,799 And energy is the ability to do work. 231 00:10:31,799 --> 00:10:33,719 And what's the unit for work? 232 00:10:33,720 --> 00:10:34,450 Well, it's joules. 233 00:10:34,450 --> 00:10:35,470 Force times distance. 234 00:10:35,470 --> 00:10:37,040 But anyway, that's a side-note. 235 00:10:37,039 --> 00:10:38,589 But it's good to know this word enthalpy. 236 00:10:38,590 --> 00:10:40,820 Especially in a chemistry context, because it's used all 237 00:10:40,820 --> 00:10:43,170 the time and it can be very confusing and non-intuitive. 238 00:10:43,169 --> 00:10:46,829 Because you're like, I don't know what enthalpy is in my 239 00:10:46,830 --> 00:10:47,460 everyday life. 240 00:10:47,460 --> 00:10:50,170 Just think of it as heat contact, because that's really 241 00:10:50,169 --> 00:10:50,909 what it is. 242 00:10:50,909 --> 00:10:55,429 But anyway, on this axis, I have heat. 243 00:10:55,429 --> 00:10:57,179 So this is when I have very little heat and I'm 244 00:10:57,179 --> 00:10:58,549 increasing my heat. 245 00:10:58,549 --> 00:11:00,404 And this is temperature. 246 00:11:00,404 --> 00:11:05,220 247 00:11:05,220 --> 00:11:09,720 Now let's say at low temperatures I'm here and as I 248 00:11:09,720 --> 00:11:12,410 add heat my temperature will go up. 249 00:11:12,409 --> 00:11:14,189 Temperature is average kinetic energy. 250 00:11:14,190 --> 00:11:16,380 Let's say I'm in the solid state here. 251 00:11:16,379 --> 00:11:18,460 And I'll do the solid state in purple. 252 00:11:18,460 --> 00:11:21,625 253 00:11:21,625 --> 00:11:23,590 No I already was using purple. 254 00:11:23,590 --> 00:11:26,490 I'll use magenta. 255 00:11:26,490 --> 00:11:29,810 So as I add heat, my temperature will go up. 256 00:11:29,809 --> 00:11:31,039 Heat is a form of energy. 257 00:11:31,039 --> 00:11:36,069 And when I add it to these molecules, as I did in this 258 00:11:36,070 --> 00:11:37,070 example, what did it do? 259 00:11:37,070 --> 00:11:38,620 It made them vibrate more. 260 00:11:38,620 --> 00:11:41,289 Or it made them have higher kinetic energy, or higher 261 00:11:41,289 --> 00:11:43,829 average kinetic engery, and that's what temperature is a 262 00:11:43,830 --> 00:11:46,860 measure of; average kinetic energy. 263 00:11:46,860 --> 00:11:50,430 So as I add heat in the solid phase, my average kinetic 264 00:11:50,429 --> 00:11:51,649 energy will go up. 265 00:11:51,649 --> 00:11:52,709 And let me write this down. 266 00:11:52,710 --> 00:11:58,930 This is in the solid phase, or the solid state of matter. 267 00:11:58,929 --> 00:12:01,059 Now something very interesting happens. 268 00:12:01,059 --> 00:12:03,929 Let's say this is water. 269 00:12:03,929 --> 00:12:09,919 So what happens at zero degrees? 270 00:12:09,919 --> 00:12:14,909 Which is also 273.15 Kelvin. 271 00:12:14,909 --> 00:12:15,829 Let's say that's that line. 272 00:12:15,830 --> 00:12:18,320 What happens to a solid? 273 00:12:18,320 --> 00:12:19,550 Well, it turns into a liquid. 274 00:12:19,549 --> 00:12:20,599 Ice melts. 275 00:12:20,600 --> 00:12:22,960 Not all solids, we're talking in particular about 276 00:12:22,960 --> 00:12:25,540 water, about H2O. 277 00:12:25,539 --> 00:12:27,990 So this is ice in our example. 278 00:12:27,990 --> 00:12:29,669 All solids aren't ice. 279 00:12:29,669 --> 00:12:33,949 Although, you could think of a rock as solid magma. 280 00:12:33,950 --> 00:12:35,200 Because that's what it is. 281 00:12:35,200 --> 00:12:38,370 282 00:12:38,370 --> 00:12:41,149 I could take that analogy a bunch of different ways. 283 00:12:41,149 --> 00:12:46,365 But the interesting thing that happens at zero degrees. 284 00:12:46,365 --> 00:12:49,180 285 00:12:49,179 --> 00:12:51,120 Depending on what direction you're going, either the 286 00:12:51,120 --> 00:12:53,730 freezing point of water or the melting point of ice, 287 00:12:53,730 --> 00:12:55,550 something interesting happens. 288 00:12:55,549 --> 00:13:00,839 As I add more heat, the temperature does not to go up. 289 00:13:00,840 --> 00:13:03,440 As I add more heat, the temperature does not go up for 290 00:13:03,440 --> 00:13:05,120 a little period. 291 00:13:05,120 --> 00:13:07,149 Let me draw that. 292 00:13:07,149 --> 00:13:10,459 For a little period, the temperature stays constant. 293 00:13:10,460 --> 00:13:14,970 And then while the temperature is constant, it stays a solid. 294 00:13:14,970 --> 00:13:16,090 We're still a solid. 295 00:13:16,090 --> 00:13:18,580 And then, we finally turn into a liquid. 296 00:13:18,580 --> 00:13:22,509 297 00:13:22,509 --> 00:13:23,960 Let's say right there. 298 00:13:23,960 --> 00:13:25,525 So we added a certain amount of heat and it 299 00:13:25,524 --> 00:13:26,590 just stayed a solid. 300 00:13:26,590 --> 00:13:28,180 But it got us to the point that the ice 301 00:13:28,179 --> 00:13:29,219 turned into a liquid. 302 00:13:29,220 --> 00:13:31,090 It was kind of melting the entire time. 303 00:13:31,090 --> 00:13:32,690 That's the best way to think about it. 304 00:13:32,690 --> 00:13:36,190 And then, once we keep adding more and more heat, then the 305 00:13:36,190 --> 00:13:37,440 liquid warms up too. 306 00:13:37,440 --> 00:13:42,450 307 00:13:42,450 --> 00:13:45,650 Now, we get to, what temperature becomes 308 00:13:45,649 --> 00:13:46,769 interesting again for water? 309 00:13:46,769 --> 00:13:56,699 Well, obviously 100 degrees Celsius or 373 degrees Kelvin. 310 00:13:56,700 --> 00:13:57,940 I'll do it in Celsius because that's what 311 00:13:57,940 --> 00:13:59,230 we're familiar with. 312 00:13:59,230 --> 00:13:59,960 What happens? 313 00:13:59,960 --> 00:14:03,889 That's the temperature at which water will vaporize or 314 00:14:03,889 --> 00:14:05,509 which water will boil. 315 00:14:05,509 --> 00:14:07,039 But something happens. 316 00:14:07,039 --> 00:14:13,299 And they're really getting kinetically active. 317 00:14:13,299 --> 00:14:16,509 But just like when you went from solid to liquid, there's 318 00:14:16,509 --> 00:14:19,990 a certain amount of energy that you have to contribute to 319 00:14:19,990 --> 00:14:20,330 the system. 320 00:14:20,330 --> 00:14:23,139 And actually, it's a good amount at this point. 321 00:14:23,139 --> 00:14:26,360 Where the water is turning into vapor, but it's not 322 00:14:26,360 --> 00:14:27,610 getting any hotter. 323 00:14:27,610 --> 00:14:31,940 324 00:14:31,940 --> 00:14:34,280 So we have to keep adding heat, but notice that the 325 00:14:34,279 --> 00:14:35,230 temperature didn't go up. 326 00:14:35,230 --> 00:14:37,070 We'll talk about it in a second what 327 00:14:37,070 --> 00:14:38,120 was happening then. 328 00:14:38,120 --> 00:14:43,060 And then finally, after that point, we're completely 329 00:14:43,059 --> 00:14:46,069 vaporized, or we're completely steam. 330 00:14:46,070 --> 00:14:48,890 Then we can start getting hot, the steam can then get hotter 331 00:14:48,889 --> 00:14:53,169 as we add more and more heat to the system. 332 00:14:53,169 --> 00:14:55,769 So the interesting question, I think it's intuitive, that as 333 00:14:55,769 --> 00:15:01,539 you add heat here, our temperature is going to go up. 334 00:15:01,539 --> 00:15:03,819 But the interesting thing is, what was going on here? 335 00:15:03,820 --> 00:15:04,879 We were adding heat. 336 00:15:04,879 --> 00:15:07,809 So over here we were turning our heat into kinetic energy. 337 00:15:07,809 --> 00:15:10,089 Temperature is average kinetic energy. 338 00:15:10,090 --> 00:15:12,710 But over here, what was our heat doing? 339 00:15:12,710 --> 00:15:15,080 Well, our heat was was not adding kinetic 340 00:15:15,080 --> 00:15:16,129 energy to the system. 341 00:15:16,129 --> 00:15:17,899 The temperature was not increasing. 342 00:15:17,899 --> 00:15:20,980 But the ice was going from ice to water. 343 00:15:20,980 --> 00:15:24,110 So what was happening at that state, is that the kinetic 344 00:15:24,110 --> 00:15:29,220 energy, the heat, was being used to essentially break 345 00:15:29,220 --> 00:15:32,190 these bonds. 346 00:15:32,190 --> 00:15:34,080 And essentially bring the molecules into a 347 00:15:34,080 --> 00:15:35,660 higher energy state. 348 00:15:35,659 --> 00:15:37,839 So you're saying, Sal, what does that mean, 349 00:15:37,840 --> 00:15:38,639 higher energy state? 350 00:15:38,639 --> 00:15:42,269 Well, if there wasn't all of this heat and all this kinetic 351 00:15:42,269 --> 00:15:44,909 energy, these molecules want to be very 352 00:15:44,909 --> 00:15:46,809 close to each other. 353 00:15:46,809 --> 00:15:49,229 For example, I want to be close to the 354 00:15:49,230 --> 00:15:50,590 surface of the earth. 355 00:15:50,590 --> 00:15:52,610 When you put me in a plane you have put me in a 356 00:15:52,610 --> 00:15:53,850 higher energy state. 357 00:15:53,850 --> 00:15:56,000 I have a lot more potential energy. 358 00:15:56,000 --> 00:15:58,799 I have the potential to fall towards the earth. 359 00:15:58,799 --> 00:16:02,629 Likewise, when you move these molecules apart, and you go 360 00:16:02,629 --> 00:16:05,570 from a solid to a liquid, they want to fall 361 00:16:05,570 --> 00:16:06,900 towards each other. 362 00:16:06,899 --> 00:16:08,850 But because they have so much kinetic energy, they never 363 00:16:08,850 --> 00:16:10,279 quite are able to do it. 364 00:16:10,279 --> 00:16:12,419 But their energy goes up. 365 00:16:12,419 --> 00:16:14,699 Their potential energy is higher because they want to 366 00:16:14,700 --> 00:16:15,960 fall towards each other. 367 00:16:15,960 --> 00:16:18,800 By falling towards each other, in theory, they 368 00:16:18,799 --> 00:16:21,009 could do some work. 369 00:16:21,009 --> 00:16:26,720 So what's happening here is, when we're contributing heat-- 370 00:16:26,720 --> 00:16:32,529 and this amount of heat we're contributing, it's called the 371 00:16:32,529 --> 00:16:33,779 heat of fusion. 372 00:16:33,779 --> 00:16:36,819 373 00:16:36,820 --> 00:16:39,010 Because it's the same amount of heat regardless how much 374 00:16:39,009 --> 00:16:40,240 direction we go in. 375 00:16:40,240 --> 00:16:43,350 When we go from solid to liquid, you view it as the 376 00:16:43,350 --> 00:16:45,450 heat of melting. 377 00:16:45,450 --> 00:16:48,040 It's the head that you need to put in to melt 378 00:16:48,039 --> 00:16:49,159 the ice into liquid. 379 00:16:49,159 --> 00:16:51,529 When you're going in this direction, it's the heat you 380 00:16:51,529 --> 00:16:55,799 have to take out of the zero degree water to 381 00:16:55,799 --> 00:16:58,039 turn it into ice. 382 00:16:58,039 --> 00:17:01,159 So you're taking that potential energy and you're 383 00:17:01,159 --> 00:17:05,049 bringing the molecules closer and closer to each other. 384 00:17:05,049 --> 00:17:08,700 So the way to think about it is, right here this heat is 385 00:17:08,700 --> 00:17:10,529 being converted to kinetic energy. 386 00:17:10,529 --> 00:17:15,019 Then, when we're at this phase change from solid to liquid, 387 00:17:15,019 --> 00:17:16,980 that heat is being used to add potential 388 00:17:16,980 --> 00:17:18,049 energy into the system. 389 00:17:18,049 --> 00:17:21,368 To pull the molecules apart, to give them 390 00:17:21,368 --> 00:17:22,419 more potential energy. 391 00:17:22,420 --> 00:17:25,060 If you pull me apart from the earth, you're giving me 392 00:17:25,059 --> 00:17:26,000 potential energy. 393 00:17:26,000 --> 00:17:29,039 Because gravity wants to pull me back to the earth. 394 00:17:29,039 --> 00:17:32,639 And I could do work when I'm falling back to the earth. 395 00:17:32,640 --> 00:17:33,770 A waterfall does work. 396 00:17:33,769 --> 00:17:35,210 It can move a turbine. 397 00:17:35,210 --> 00:17:37,625 You could have a bunch of falling Sals move 398 00:17:37,625 --> 00:17:39,160 a turbine as well. 399 00:17:39,160 --> 00:17:42,050 And then, once you are fully a liquid, then you just become a 400 00:17:42,049 --> 00:17:43,440 warmer and warmer liquid. 401 00:17:43,440 --> 00:17:48,759 Now the heat is, once again, being used for kinetic energy. 402 00:17:48,759 --> 00:17:51,009 You're making the water molecules move past each other 403 00:17:51,009 --> 00:17:53,190 faster, and faster, and faster. 404 00:17:53,190 --> 00:17:57,630 To some point where they want to completely disassociate 405 00:17:57,630 --> 00:17:58,580 from each other. 406 00:17:58,579 --> 00:18:00,369 They want to not even slide past each other, just 407 00:18:00,369 --> 00:18:03,079 completely jump away from each other. 408 00:18:03,079 --> 00:18:04,139 And that's right here. 409 00:18:04,140 --> 00:18:05,610 This is the heat of vaporization. 410 00:18:05,609 --> 00:18:13,879 411 00:18:13,880 --> 00:18:15,440 And the same idea is happening. 412 00:18:15,440 --> 00:18:17,710 Before we were sliding next to each other, now we're pulling 413 00:18:17,710 --> 00:18:19,509 apart altogether. 414 00:18:19,509 --> 00:18:22,619 So they could definitely fall closer together. 415 00:18:22,619 --> 00:18:27,509 And then once we've added this much heat, now we're just 416 00:18:27,509 --> 00:18:28,650 heating up the steam. 417 00:18:28,650 --> 00:18:30,990 We're just heating up the gaseous water. 418 00:18:30,990 --> 00:18:33,769 And it's just getting hotter and hotter and hotter. 419 00:18:33,769 --> 00:18:35,670 But the interesting thing there, and I mean at least the 420 00:18:35,670 --> 00:18:41,039 interesting thing to me when I first learned this, whenever I 421 00:18:41,039 --> 00:18:43,970 think of zero degrees water I'll say, oh it must be ice. 422 00:18:43,970 --> 00:18:45,589 But that's not necessarily the case. 423 00:18:45,589 --> 00:18:48,679 If you start with water and you make it colder and colder 424 00:18:48,680 --> 00:18:52,460 and colder to zero degrees, you're essentially taking heat 425 00:18:52,460 --> 00:18:53,440 out of the water. 426 00:18:53,440 --> 00:18:57,410 You can have zero degree water and it hasn't 427 00:18:57,410 --> 00:18:58,660 turned into ice yet. 428 00:18:58,660 --> 00:19:01,850 And likewise, you could have 100 degree water that hasn't 429 00:19:01,849 --> 00:19:03,069 turned into steam yeat. 430 00:19:03,069 --> 00:19:04,200 You have to add more energy. 431 00:19:04,200 --> 00:19:05,799 You can also have 100 degree steam. 432 00:19:05,799 --> 00:19:08,700 You can also have zero degree water. 433 00:19:08,700 --> 00:19:10,680 Anyway, hopefully that gives you a little bit of intuition 434 00:19:10,680 --> 00:19:12,740 of what the different states of matter are. 435 00:19:12,740 --> 00:19:15,180 And in the next problem, we'll talk about how much heat 436 00:19:15,180 --> 00:19:18,130 exactly it does take to move along this line. 437 00:19:18,130 --> 00:19:21,020 And maybe we can solve some problems on how much ice we 438 00:19:21,019 --> 00:19:23,619 might need to make our drink cool.