1 00:00:11,510 --> 00:00:12,172 SHAWN: OK. 2 00:00:12,172 --> 00:00:13,130 Good morning, everyone. 3 00:00:13,130 --> 00:00:16,896 Welcome to the recitation section of 10.213. 4 00:00:16,896 --> 00:00:18,848 This is the agenda for today. 5 00:00:24,710 --> 00:00:26,660 So first of all, we will review the concept 6 00:00:26,660 --> 00:00:28,600 of the physical state of a substance. 7 00:00:36,360 --> 00:00:38,820 And secondly, we're going to talk about phase diagramming. 8 00:00:46,200 --> 00:00:49,050 First of all, the physical state is a state 9 00:00:49,050 --> 00:00:51,870 that a molecule can exist in reality. 10 00:00:51,870 --> 00:00:54,380 So take water as an example. 11 00:00:54,380 --> 00:00:59,994 Water can exist as gas, liquid, and-- 12 00:00:59,994 --> 00:01:00,660 STUDENTS: Solid. 13 00:01:00,660 --> 00:01:01,320 SHAWN: Solid. 14 00:01:01,320 --> 00:01:02,100 Correct. 15 00:01:02,100 --> 00:01:06,135 So a phase diagram is a tool for engineers or scientists 16 00:01:06,135 --> 00:01:10,910 to interpret or very easily identify the physical state 17 00:01:10,910 --> 00:01:13,436 at a certain temperature and pressure. 18 00:01:13,436 --> 00:01:17,170 So we have this diagram. 19 00:01:17,170 --> 00:01:24,832 And on the horizontal axis is temperature, 20 00:01:24,832 --> 00:01:27,826 with a unit of Celsius. 21 00:01:27,826 --> 00:01:34,830 And on the vertical axis, we have pressure, 22 00:01:34,830 --> 00:01:37,371 with a unit of pascals. 23 00:01:37,371 --> 00:01:38,682 OK? 24 00:01:38,682 --> 00:01:42,620 As we just talked about, we have three different states of water 25 00:01:42,620 --> 00:01:44,270 exist in this diagram. 26 00:01:44,270 --> 00:01:48,010 At high temperature-- this is the high-temperature phase-- 27 00:01:48,010 --> 00:01:52,104 low pressure, water will exist as-- 28 00:01:52,104 --> 00:01:53,020 STUDENTS: Gas. 29 00:01:53,020 --> 00:01:54,395 SHAWN: Correct. 30 00:01:54,395 --> 00:01:56,110 So this is the gas state. 31 00:01:56,110 --> 00:02:01,624 And at low temperature, high pressure, what do we exist as? 32 00:02:01,624 --> 00:02:02,290 STUDENTS: Solid. 33 00:02:02,290 --> 00:02:03,170 SHAWN: Solid? 34 00:02:03,170 --> 00:02:05,610 Great. 35 00:02:05,610 --> 00:02:11,210 And at moderate temperature and pressure, 36 00:02:11,210 --> 00:02:13,285 water will exist as liquid. 37 00:02:13,285 --> 00:02:16,260 That's what we usually see in reality. 38 00:02:16,260 --> 00:02:21,218 And there are a lot of-- there are some-- sorry. 39 00:02:24,400 --> 00:02:26,790 Some of the components in this phase 40 00:02:26,790 --> 00:02:33,110 diagram you have to identify the physical state of the matter 41 00:02:33,110 --> 00:02:39,170 and also when they transform from one state to another. 42 00:02:39,170 --> 00:02:43,470 So we have three different lines here. 43 00:02:43,470 --> 00:02:47,150 So each line represents a certain condition 44 00:02:47,150 --> 00:02:50,430 that two phases can coexist. 45 00:02:50,430 --> 00:03:12,420 So for example, at 100 Celsius and 101.325 kilopascals-- so 46 00:03:12,420 --> 00:03:15,170 at this specific pressure and temperature, 47 00:03:15,170 --> 00:03:19,435 water can exist as gas and liquid simultaneously. 48 00:03:19,435 --> 00:03:21,552 So far, so clear? 49 00:03:21,552 --> 00:03:23,520 OK. 50 00:03:23,520 --> 00:03:28,670 And there's an intersecting point of these three lines. 51 00:03:28,670 --> 00:03:31,488 This intersecting point is called a triple point. 52 00:03:37,950 --> 00:03:42,100 At this triple point, we have three phases coexist. 53 00:03:42,100 --> 00:03:48,127 So solid, liquid, and gas can exist at this specific pressure 54 00:03:48,127 --> 00:03:49,121 and temperature. 55 00:03:52,110 --> 00:03:52,630 OK. 56 00:03:52,630 --> 00:03:54,810 So now there's a question. 57 00:03:54,810 --> 00:03:57,334 Supposedly you're on the mountain of Himalaya 58 00:03:57,334 --> 00:03:59,870 and then you know the pressure is 59 00:03:59,870 --> 00:04:02,762 slightly lower than 1 atmosphere, which 60 00:04:02,762 --> 00:04:06,130 is less than 1.1 kilopascal. 61 00:04:06,130 --> 00:04:11,390 My question is, is the water going to boil at 100 Celsius? 62 00:04:11,390 --> 00:04:16,528 Or is it going to boil below or above 100 Celsius? 63 00:04:16,528 --> 00:04:21,488 Anyone that volunteer a guess? 64 00:04:21,488 --> 00:04:22,302 Melissa? 65 00:04:22,302 --> 00:04:23,968 STUDENTS: It would be below 100 Celsius. 66 00:04:23,968 --> 00:04:24,464 SHAWN: OK. 67 00:04:24,464 --> 00:04:24,960 Why? 68 00:04:24,960 --> 00:04:26,960 STUDENTS: Because if you're at a lower pressure, 69 00:04:26,960 --> 00:04:29,672 you'll intersect the coexistence line between liquid and gas 70 00:04:29,672 --> 00:04:30,783 at a lower temperature. 71 00:04:30,783 --> 00:04:31,408 SHAWN: Correct. 72 00:04:31,408 --> 00:04:31,908 Excellent. 73 00:04:34,900 --> 00:04:36,729 Does anyone follow her? 74 00:04:36,729 --> 00:04:37,228 OK. 75 00:04:37,228 --> 00:04:39,450 Great. 76 00:04:39,450 --> 00:04:42,540 So let me just wrap up today's lesson. 77 00:04:42,540 --> 00:04:46,130 We first reviewed the physical state of water. 78 00:04:46,130 --> 00:04:48,780 Water can exist as liquid, solid, and gas 79 00:04:48,780 --> 00:04:51,400 depending on the temperature and pressure. 80 00:04:51,400 --> 00:04:53,397 And then we drew the phase diagram of water. 81 00:04:53,397 --> 00:04:55,272 And there are three different elements there, 82 00:04:55,272 --> 00:04:56,620 which you'll remember. 83 00:04:56,620 --> 00:05:00,450 First, in each space, you have the phase of water. 84 00:05:00,450 --> 00:05:06,570 And then we have the coexisting lines, which is the lines 85 00:05:06,570 --> 00:05:10,300 that water can exist as two different phases 86 00:05:10,300 --> 00:05:11,224 simultaneously. 87 00:05:11,224 --> 00:05:13,440 And then we have the triple point, 88 00:05:13,440 --> 00:05:16,035 where three different phases can coexist. 89 00:05:16,035 --> 00:05:17,480 OK. 90 00:05:17,480 --> 00:05:18,760 Any questions for today? 91 00:05:24,084 --> 00:05:26,020 OK. 92 00:05:26,020 --> 00:05:27,330 So this is for today. 93 00:05:27,330 --> 00:05:30,720 Next time, we will talk about phase diagrams of a mixture. 94 00:05:30,720 --> 00:05:34,350 For example, if you add sodium chloride, which is salt, 95 00:05:34,350 --> 00:05:38,340 in water, how does the phase diagram of water change? 96 00:05:38,340 --> 00:05:40,170 If you want to know that, definitely 97 00:05:40,170 --> 00:05:42,740 come to our next recitation section. 98 00:05:42,740 --> 00:05:44,470 Thank you.