1 00:00:00,000 --> 00:00:00,830 2 00:00:00,830 --> 00:00:03,669 All of the phase changes we've been doing so far have been 3 00:00:03,669 --> 00:00:05,980 under constant pressure conditions, and, in 4 00:00:05,980 --> 00:00:07,940 particular, with the problems that I've been doing with 5 00:00:07,940 --> 00:00:11,480 water phase changes in the last couple of videos, it was 6 00:00:11,480 --> 00:00:14,330 at atmospheric pressure, at least at sea level atmospheric 7 00:00:14,330 --> 00:00:15,859 pressure, or at 1 atmosphere. 8 00:00:15,859 --> 00:00:17,289 So it was done-- well, I'll explain this 9 00:00:17,289 --> 00:00:18,449 diagram in a second. 10 00:00:18,449 --> 00:00:21,140 But we all know that in the universe, pressure isn't 11 00:00:21,140 --> 00:00:23,190 always constant and it definitely isn't always 12 00:00:23,190 --> 00:00:24,460 constant at 1 atmosphere. 13 00:00:24,460 --> 00:00:27,060 1 atmosphere was defined as the pressure at 14 00:00:27,059 --> 00:00:28,079 sea level on Earth. 15 00:00:28,079 --> 00:00:31,320 Obviously, pressure will vary wildly if you go to smaller 16 00:00:31,320 --> 00:00:35,460 planets or larger planets, or have thicker atmospheres, or 17 00:00:35,460 --> 00:00:38,640 if we're just doing different types of applications dealing 18 00:00:38,640 --> 00:00:40,660 with gases and liquids and solids. 19 00:00:40,659 --> 00:00:45,459 So what I've drawn here is a phase diagram. 20 00:00:45,460 --> 00:00:46,710 Let me write that down. 21 00:00:46,710 --> 00:00:50,480 22 00:00:50,479 --> 00:00:53,929 And there are many forms of phase diagrams. This is the 23 00:00:53,929 --> 00:00:56,479 most common form that you might see in your chemistry 24 00:00:56,479 --> 00:01:00,199 class or on some standardized test, but what it captures is 25 00:01:00,200 --> 00:01:03,240 the different states of matter and when they transition 26 00:01:03,240 --> 00:01:05,590 according to temperature and pressure. 27 00:01:05,590 --> 00:01:08,010 This is the phase diagram for water. 28 00:01:08,010 --> 00:01:11,870 So just to understand what's going on here, is that on this 29 00:01:11,870 --> 00:01:13,484 axis, I have pressure. 30 00:01:13,484 --> 00:01:16,519 31 00:01:16,519 --> 00:01:19,629 On the x-axis, I have temperature, and at any given 32 00:01:19,629 --> 00:01:21,649 point, this diagram will tell you whether you're dealing 33 00:01:21,650 --> 00:01:27,690 with a solid, so solid will be here, a liquid will 34 00:01:27,689 --> 00:01:34,159 be here, or a gas. 35 00:01:34,159 --> 00:01:42,159 For example, if I told you that I was at 0 degrees, let's 36 00:01:42,159 --> 00:01:47,340 say 0 degrees is right there, if I'm at 0 degrees Celsius 37 00:01:47,340 --> 00:01:49,820 and 1 atmosphere, where am I? 38 00:01:49,819 --> 00:01:52,399 So 0 degrees, 1 atmosphere, I'm right at 39 00:01:52,400 --> 00:01:53,710 that point right there. 40 00:01:53,709 --> 00:01:58,000 So I'm at a boundary point between solids and liquids at 41 00:01:58,000 --> 00:02:00,769 1 atmosphere of pressure, right? 42 00:02:00,769 --> 00:02:04,549 This is when we're at 1 atmosphere of pressure. 43 00:02:04,549 --> 00:02:08,349 So this coincides with our traditional notion of when ice 44 00:02:08,349 --> 00:02:10,978 freezes or when it melts at 0 degrees. 45 00:02:10,979 --> 00:02:16,290 If we made the pressure higher, what happens? 46 00:02:16,289 --> 00:02:20,340 Well, then ice starts melting at a lower temperature, right? 47 00:02:20,340 --> 00:02:22,990 So this is pressure going up, so pressure going up, let's 48 00:02:22,990 --> 00:02:24,400 say-- I don't know what this is. 49 00:02:24,400 --> 00:02:29,289 This is maybe 10 atmospheres, ten times Earth's atmospheric 50 00:02:29,289 --> 00:02:31,549 pressure at sea level, then all of a sudden, the 51 00:02:31,550 --> 00:02:34,670 temperature at which solid turns into liquid-- this 52 00:02:34,669 --> 00:02:37,750 transition is solid to liquid --the temperature at which 53 00:02:37,750 --> 00:02:39,789 that happens will go down. 54 00:02:39,789 --> 00:02:42,479 Likewise, if we lower the pressure, if we go to Denver 55 00:02:42,479 --> 00:02:45,819 and it's a mile high, pressure is lower because we have less 56 00:02:45,819 --> 00:02:51,079 of the atmosphere above us, then all of a sudden, the 57 00:02:51,080 --> 00:02:54,990 freezing point increases, so the freezing point will be 58 00:02:54,990 --> 00:02:57,020 something above 1 degree. 59 00:02:57,020 --> 00:03:00,520 This isn't drawn completely to scale, but the idea is your 60 00:03:00,520 --> 00:03:03,610 ice would actually freeze a little bit faster and would 61 00:03:03,610 --> 00:03:08,740 freeze at a higher temperature in Denver than it would at the 62 00:03:08,740 --> 00:03:15,840 bottom of the Dead Sea or in Death Valley at some below sea 63 00:03:15,840 --> 00:03:18,210 level point on the planet. 64 00:03:18,210 --> 00:03:21,550 Now, this transition is the transition between 65 00:03:21,550 --> 00:03:23,230 anything and gas. 66 00:03:23,229 --> 00:03:24,819 And we're very familiar, this is 1 atmosphere. 67 00:03:24,819 --> 00:03:26,789 And remember, this is water we're dealing with. 68 00:03:26,789 --> 00:03:29,519 This is the diagram for water, so at 1 atmosphere, this is 69 00:03:29,520 --> 00:03:31,530 kind of the stuff that we're used to seeing. 70 00:03:31,530 --> 00:03:33,909 Let me draw a line here. 71 00:03:33,909 --> 00:03:41,430 So at 1 atmosphere, 0 degrees is where solid, or ice, turns 72 00:03:41,430 --> 00:03:42,780 into liquid water. 73 00:03:42,780 --> 00:03:45,669 And then we go up here, so we keep going at a higher, 74 00:03:45,669 --> 00:03:48,679 higher, higher temperature, and then here, this would be, 75 00:03:48,680 --> 00:03:54,550 since we're at 1 atmosphere, this is 100 degrees Celsius 76 00:03:54,550 --> 00:03:55,480 right there. 77 00:03:55,479 --> 00:03:59,500 And that's the point at 1 atmosphere of pressure where 78 00:03:59,500 --> 00:04:02,849 liquid turns into gas, or water vaporizes, 79 00:04:02,849 --> 00:04:04,030 or the liquid boils. 80 00:04:04,030 --> 00:04:07,020 All of those are acceptable ways to think about that. 81 00:04:07,020 --> 00:04:08,760 But what happens when we go to low pressure? 82 00:04:08,759 --> 00:04:11,679 Once again, let's take our little trip to Denver. 83 00:04:11,680 --> 00:04:14,740 So that's Denver right there. 84 00:04:14,740 --> 00:04:15,969 It's not that drastic. 85 00:04:15,969 --> 00:04:19,500 I'm just doing that for education purposes. 86 00:04:19,500 --> 00:04:25,029 Or even better, let's say Mount Everest. Mount Everest, 87 00:04:25,029 --> 00:04:26,399 very low pressure there. 88 00:04:26,399 --> 00:04:29,120 Then our freezing point, we already said that goes up when 89 00:04:29,120 --> 00:04:31,840 you lower the pressure, and your boiling point goes down, 90 00:04:31,839 --> 00:04:36,039 so it's much easier to boil something on the top of Mount 91 00:04:36,040 --> 00:04:39,870 Everest than it is to boil it at the bottom or at the lowest 92 00:04:39,870 --> 00:04:43,740 point in Death Valley or the Dead Sea. 93 00:04:43,740 --> 00:04:50,750 The intuition behind that is if I have a liquid, a bunch of 94 00:04:50,750 --> 00:04:55,769 molecules in liquid form, and they're touching each other, 95 00:04:55,769 --> 00:04:58,319 but they have enough kinetic energy to move past each 96 00:04:58,319 --> 00:05:02,659 other, so they're flowing past each other, they're kind of 97 00:05:02,660 --> 00:05:06,170 rubbing up against each other, one of the reasons why they 98 00:05:06,170 --> 00:05:09,620 don't just evaporate, why this guy doesn't just jump up 99 00:05:09,620 --> 00:05:10,910 there, is that there's air above him. 100 00:05:10,910 --> 00:05:12,500 There's air pressure. 101 00:05:12,500 --> 00:05:14,569 And air pressure, we've learned about this 102 00:05:14,569 --> 00:05:15,980 when we did PV nRT. 103 00:05:15,980 --> 00:05:19,430 That's a bunch of gas molecules, and the pressure 104 00:05:19,430 --> 00:05:21,129 they're creating is essentially caused by their 105 00:05:21,129 --> 00:05:22,659 temperature and their kinetic energy. 106 00:05:22,660 --> 00:05:27,290 And they sit there, and they bounce, and they essentially 107 00:05:27,290 --> 00:05:30,569 keep these heavier molecules from going up. 108 00:05:30,569 --> 00:05:34,259 They keep them from essentially separating from 109 00:05:34,259 --> 00:05:35,610 each other and turning into a gas. 110 00:05:35,610 --> 00:05:39,379 So the more pressure you have, the harder it is for these 111 00:05:39,379 --> 00:05:40,250 guys to escape. 112 00:05:40,250 --> 00:05:43,279 On the other hand, if we're in a vacuum, if we're doing this 113 00:05:43,279 --> 00:05:46,119 on the surface of the moon and there's none of these guys 114 00:05:46,120 --> 00:05:47,889 there, then just a little slight bump. 115 00:05:47,889 --> 00:05:50,709 Even though this guy's still a little bit attracted to over 116 00:05:50,709 --> 00:05:52,750 here, they're still attracted to each other. 117 00:05:52,750 --> 00:05:54,980 But just a little bit of bump, since there's no pressure up 118 00:05:54,980 --> 00:05:58,259 here on the surface of the moon, might allow this guy to 119 00:05:58,259 --> 00:06:01,839 escape and go straight to a gas. 120 00:06:01,839 --> 00:06:04,669 So when you lower the pressure, it's just that much 121 00:06:04,670 --> 00:06:08,189 easier to go from liquid to gas or even from solid to gas. 122 00:06:08,189 --> 00:06:09,670 And you might say, Sal, that's a bizarre 123 00:06:09,670 --> 00:06:10,960 concept, solid to gas. 124 00:06:10,959 --> 00:06:14,259 It turns out, if you get to low enough pressures here, I 125 00:06:14,259 --> 00:06:16,649 mean, let's say this is-- Actually, there's probably not 126 00:06:16,649 --> 00:06:17,019 stuff here. 127 00:06:17,019 --> 00:06:19,979 This is probably close to a vacuum right here. 128 00:06:19,980 --> 00:06:23,000 You could go from ice-- So if you took ice and you were on 129 00:06:23,000 --> 00:06:26,120 the moon and you were at the right temperature-- this is 130 00:06:26,120 --> 00:06:29,800 maybe some negative degrees Celsius temperature; I don't 131 00:06:29,800 --> 00:06:32,210 know what the exact temperature is --your ice on 132 00:06:32,209 --> 00:06:36,279 the moon would go directly from ice to a gas. 133 00:06:36,279 --> 00:06:38,849 Because there's this huge vacuum here, so these 134 00:06:38,850 --> 00:06:41,520 molecules would say, hey, there's all this space to fill 135 00:06:41,519 --> 00:06:43,289 and if they just get bumped a little bit, they're just going 136 00:06:43,290 --> 00:06:45,230 to escape and turn into a gas. 137 00:06:45,230 --> 00:06:47,879 You might say, oh, Sal, that's a strange phenomenon. 138 00:06:47,879 --> 00:06:49,379 It only exists on the moon. 139 00:06:49,379 --> 00:06:53,449 And to rebut that comment, I've drawn the phase diagram 140 00:06:53,449 --> 00:06:54,699 for carbon dioxide. 141 00:06:54,699 --> 00:06:58,259 142 00:06:58,259 --> 00:06:59,149 It's all around you. 143 00:06:59,149 --> 00:07:00,589 You're exhaling it as we speak. 144 00:07:00,589 --> 00:07:03,949 Your plants in the room are hopefully inhaling it, but 145 00:07:03,949 --> 00:07:06,899 carbon dioxide at 1 atmosphere has a very different behavior 146 00:07:06,899 --> 00:07:07,929 than water. 147 00:07:07,930 --> 00:07:09,600 This is carbon dioxide at 1 atmosphere. 148 00:07:09,600 --> 00:07:12,050 Just so you know, this scale is definitely 149 00:07:12,050 --> 00:07:13,020 not drawn to scale. 150 00:07:13,019 --> 00:07:15,229 The difference between 1 atmosphere and 5 atmospheres 151 00:07:15,230 --> 00:07:18,170 is not the same as between 5 atmospheres and 73. 152 00:07:18,170 --> 00:07:21,530 Likewise, this is not drawn to scale here. 153 00:07:21,529 --> 00:07:23,679 This is a much larger distance than this. 154 00:07:23,680 --> 00:07:25,650 If I had to really draw it to scale, I'd have to stretch 155 00:07:25,649 --> 00:07:27,179 this chart out or do a 156 00:07:27,180 --> 00:07:29,100 logarithmic chart or something. 157 00:07:29,100 --> 00:07:32,030 But anyway, I was talking about carbon dioxide. 158 00:07:32,029 --> 00:07:36,339 So this is carbon dioxide solid, and this is gas, and 159 00:07:36,339 --> 00:07:39,879 this is liquid carbon dioxide. 160 00:07:39,879 --> 00:07:46,120 So at 1 atmosphere, let's say you live at sea level, like 161 00:07:46,120 --> 00:07:48,605 you're in New Orleans, I guess that's a little bit below sea 162 00:07:48,605 --> 00:07:51,390 level-- that's where I grew up --if you were able to get your 163 00:07:51,389 --> 00:07:55,560 fridge down to minus 80 degrees Celsius, the carbon 164 00:07:55,560 --> 00:07:57,530 dioxide would actually freeze. 165 00:07:57,529 --> 00:07:59,819 And you're actually not too unfamiliar with that, or at 166 00:07:59,819 --> 00:08:02,319 least you haven't been if you've gone to some-- I don't 167 00:08:02,319 --> 00:08:05,870 know if they still use it for smoke machines or for visual 168 00:08:05,870 --> 00:08:10,730 effects on stage, but this is dry ice. 169 00:08:10,730 --> 00:08:14,819 It's frozen carbon dioxide. 170 00:08:14,819 --> 00:08:19,180 If you're at sea level atmospheric pressure, as soon 171 00:08:19,180 --> 00:08:22,889 as you get above this minus 78 and 1/2 degrees Celsius, it 172 00:08:22,889 --> 00:08:24,990 sublimates to gas. 173 00:08:24,990 --> 00:08:28,560 So that process, where you go straight from a solid to a 174 00:08:28,560 --> 00:08:29,810 gas, is sublimation. 175 00:08:29,810 --> 00:08:33,259 176 00:08:33,259 --> 00:08:35,928 And that's why dry ice, when you see it, you don't see 177 00:08:35,928 --> 00:08:39,000 liquid dry ice or you don't see it at standard pressures. 178 00:08:39,000 --> 00:08:42,110 I've never seen liquid carbon dioxide. 179 00:08:42,110 --> 00:08:45,590 In fact, to get liquid carbon dioxide, you have to get above 180 00:08:45,590 --> 00:08:49,030 5 atmospheres so you have to get above five times the sea 181 00:08:49,029 --> 00:08:50,899 level pressure on Earth, and you're really not going to see 182 00:08:50,899 --> 00:08:52,669 that in natural conditions on Earth. 183 00:08:52,669 --> 00:08:54,740 You might see that on Jupiter or Saturn where you have 184 00:08:54,740 --> 00:08:57,330 tremendous pressures because of the gravity and all of the 185 00:08:57,330 --> 00:08:59,710 atmosphere above you. 186 00:08:59,710 --> 00:09:01,680 Liquid carbon dioxide, you might see-- I don't know if 187 00:09:01,679 --> 00:09:03,629 Jupiter actually has carbon, but you'll probably see it on 188 00:09:03,629 --> 00:09:06,960 other huge massive planets that are gas giants. 189 00:09:06,960 --> 00:09:10,379 But on Earth, this process is just called sublimation. 190 00:09:10,379 --> 00:09:11,250 It's just a neat word. 191 00:09:11,250 --> 00:09:12,740 Or it's sublimating. 192 00:09:12,740 --> 00:09:15,460 It's going straight from solid to gas and it's something 193 00:09:15,460 --> 00:09:16,920 you've seen with dry ice. 194 00:09:16,919 --> 00:09:18,819 Now, there's a couple other interesting points here and 195 00:09:18,820 --> 00:09:20,920 you're probably already noticing them. 196 00:09:20,919 --> 00:09:24,000 This right here is called the triple point, because right 197 00:09:24,000 --> 00:09:27,480 here at this-- Well, in the case of carbon dioxide, at 5 198 00:09:27,480 --> 00:09:32,129 atmospheres and minus 56 degrees Celsius, the carbon 199 00:09:32,129 --> 00:09:36,960 dioxide is in a state of equilibrium between the ice, 200 00:09:36,960 --> 00:09:38,540 the liquid and the gas. 201 00:09:38,539 --> 00:09:40,329 It's a little bit of all of the three. 202 00:09:40,330 --> 00:09:43,030 And if you just nudge it in one direction or another by 203 00:09:43,029 --> 00:09:44,549 nudging the pressure or the temperature, 204 00:09:44,549 --> 00:09:46,449 it'll go in that direction. 205 00:09:46,450 --> 00:09:50,600 Similarly, water's triple point is right here. 206 00:09:50,600 --> 00:09:52,379 It's at a much lower pressure than we're 207 00:09:52,379 --> 00:09:53,269 used to dealing with. 208 00:09:53,269 --> 00:10:01,039 This is 0.611 kilopascals, or just 611 pascals, which is 209 00:10:01,039 --> 00:10:03,500 5/1000 of an atmosphere. 210 00:10:03,500 --> 00:10:06,429 So if you go down to 5/1000 of an atmosphere and you go a 211 00:10:06,429 --> 00:10:10,750 little bit above 0 degrees Celsius, you're at the triple 212 00:10:10,750 --> 00:10:11,700 point of water. 213 00:10:11,700 --> 00:10:15,210 where water can take on any of these states if you just nudge 214 00:10:15,210 --> 00:10:16,790 it in one direction or another. 215 00:10:16,789 --> 00:10:18,730 Now, the other interesting point on these 216 00:10:18,730 --> 00:10:20,680 charts is up here. 217 00:10:20,679 --> 00:10:22,709 This is the critical point. 218 00:10:22,710 --> 00:10:24,389 Sounds very important. 219 00:10:24,389 --> 00:10:25,439 Critical point. 220 00:10:25,440 --> 00:10:27,730 And that's the point at which if you increase the 221 00:10:27,730 --> 00:10:31,190 temperature beyond that or the pressure beyond that, you're 222 00:10:31,190 --> 00:10:35,140 dealing with a supercritical fluid. 223 00:10:35,139 --> 00:10:37,029 It sounds very exciting. 224 00:10:37,029 --> 00:10:41,600 So above here, you have a supercritical fluid. 225 00:10:41,600 --> 00:10:45,600 So very high temperature, very high pressure. 226 00:10:45,600 --> 00:10:48,290 It's so high temperature that it wants to be a gas, but 227 00:10:48,289 --> 00:10:49,929 you're putting so much pressure on it that it wants 228 00:10:49,929 --> 00:10:52,059 to be a fluid, so it's a little bit of both. 229 00:10:52,059 --> 00:10:55,269 And actually, in the case of water, supercritical water is 230 00:10:55,269 --> 00:10:56,929 actually used as a solvent. 231 00:10:56,929 --> 00:10:59,799 Because you can imagine, it's kind of like liquid water in 232 00:10:59,799 --> 00:11:02,209 that things can dissolve in it, but it's so high 233 00:11:02,210 --> 00:11:05,300 temperature and it can diffuse into solids that it's really 234 00:11:05,299 --> 00:11:08,439 good at just getting whatever you want out of whatever 235 00:11:08,440 --> 00:11:15,490 you're trying to clean or somehow get into or get salt 236 00:11:15,490 --> 00:11:16,850 put into the water. 237 00:11:16,850 --> 00:11:19,450 So this is supercritical fluid and it's a fun 238 00:11:19,450 --> 00:11:20,190 thing to think about. 239 00:11:20,190 --> 00:11:24,150 But anyway, I just wanted to expose you to these phase 240 00:11:24,149 --> 00:11:28,230 diagrams. Everything I've done so far was at a constant 241 00:11:28,230 --> 00:11:30,139 pressure and I changed the temperature, but you can also 242 00:11:30,139 --> 00:11:31,319 read them the other way. 243 00:11:31,320 --> 00:11:35,530 If I'm at 100 degrees, and I go from-- Well, let's say I'm 244 00:11:35,529 --> 00:11:40,730 at 110 degrees, where at sea level is comfortably in the 245 00:11:40,730 --> 00:11:44,590 gaseous phase for-- So this is 110 degrees for water. 246 00:11:44,590 --> 00:11:45,649 It's water vapor. 247 00:11:45,649 --> 00:11:48,889 But if I were to increase the pressure and I keep increasing 248 00:11:48,889 --> 00:11:51,730 the pressure and maybe I dig a hole or something or I go into 249 00:11:51,730 --> 00:11:58,120 the ocean, then it's going to condense into water or it's 250 00:11:58,120 --> 00:11:59,259 going to condense into a liquid. 251 00:11:59,259 --> 00:12:06,549 If I did that experiment here, when I increase the pressure, 252 00:12:06,549 --> 00:12:09,500 I'm going to reverse sublimate. 253 00:12:09,500 --> 00:12:11,710 And I think I wrote down a word for what that is. 254 00:12:11,710 --> 00:12:12,980 Let me see if I wrote it down someplace. 255 00:12:12,980 --> 00:12:13,840 Oh, no, I didn't. 256 00:12:13,840 --> 00:12:14,980 I didn't write it down. 257 00:12:14,980 --> 00:12:19,210 But essentially it's something like condense, but the word is 258 00:12:19,210 --> 00:12:20,480 escaping me at the second. 259 00:12:20,480 --> 00:12:21,769 It's something on the word of 260 00:12:21,769 --> 00:12:23,519 condensing or falling together. 261 00:12:23,519 --> 00:12:27,289 Anyway, I forget the word, but it'll go straight from a gas 262 00:12:27,289 --> 00:12:28,269 to a solid. 263 00:12:28,269 --> 00:12:30,110 So these are pretty neat diagrams. They actually tell a 264 00:12:30,110 --> 00:12:32,830 lot about different substances and then tell you what happens 265 00:12:32,830 --> 00:12:35,450 when the pressure or the temperature changes.