[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.41,0:00:01.67,Default,,0000,0000,0000,,有个反应是
Dialogue: 0,0:00:01.69,0:00:03.42,Default,,0000,0000,0000,,1mol的甲烷
Dialogue: 0,0:00:03.43,0:00:05.59,Default,,0000,0000,0000,,和2mol的氧气反应
Dialogue: 0,0:00:05.61,0:00:08.22,Default,,0000,0000,0000,,会生成1mol的二氧化碳
Dialogue: 0,0:00:08.24,0:00:09.43,Default,,0000,0000,0000,,和2mol的水
Dialogue: 0,0:00:09.44,0:00:11.63,Default,,0000,0000,0000,,这集里 我们想判断
Dialogue: 0,0:00:11.65,0:00:14.94,Default,,0000,0000,0000,,这个反应是不是自发的
Dialogue: 0,0:00:14.96,0:00:16.20,Default,,0000,0000,0000,,上次我们已经学过
Dialogue: 0,0:00:16.21,0:00:17.75,Default,,0000,0000,0000,,怎么判断自发性啦
Dialogue: 0,0:00:17.76,0:00:19.70,Default,,0000,0000,0000,,这时候就要利用吉布斯自由能
Dialogue: 0,0:00:19.71,0:00:21.33,Default,,0000,0000,0000,,或吉布斯自由能变啦
Dialogue: 0,0:00:21.34,0:00:23.52,Default,,0000,0000,0000,,而吉布斯自由能变ΔG
Dialogue: 0,0:00:23.53,0:00:28.14,Default,,0000,0000,0000,,等于反应的焓变ΔH
Dialogue: 0,0:00:28.16,0:00:30.70,Default,,0000,0000,0000,,减去反应的温度T
Dialogue: 0,0:00:30.71,0:00:32.82,Default,,0000,0000,0000,,乘以熵变ΔS
Dialogue: 0,0:00:32.84,0:00:35.01,Default,,0000,0000,0000,,如果ΔG<0
Dialogue: 0,0:00:35.03,0:00:39.40,Default,,0000,0000,0000,,那反应就是自发的了
Dialogue: 0,0:00:39.41,0:00:41.86,Default,,0000,0000,0000,,我先给大伙开个好头
Dialogue: 0,0:00:41.88,0:00:44.04,Default,,0000,0000,0000,,我刚刚已经把
Dialogue: 0,0:00:44.06,0:00:46.08,Default,,0000,0000,0000,,反应的焓变算出来了
Dialogue: 0,0:00:46.09,0:00:47.46,Default,,0000,0000,0000,,就在这里呢
Dialogue: 0,0:00:47.48,0:00:48.44,Default,,0000,0000,0000,,大家都知道怎么求ΔH了吧
Dialogue: 0,0:00:48.45,0:00:50.17,Default,,0000,0000,0000,,几集前我们讲过的
Dialogue: 0,0:00:50.18,0:00:52.36,Default,,0000,0000,0000,,先查出来每个产物的
Dialogue: 0,0:00:52.38,0:00:54.48,Default,,0000,0000,0000,,生成热
Dialogue: 0,0:00:54.49,0:00:56.65,Default,,0000,0000,0000,,例如水 你要把生成热乘以2
Dialogue: 0,0:00:56.67,0:00:58.17,Default,,0000,0000,0000,,因为反应生成了2mol的水
Dialogue: 0,0:00:58.18,0:01:00.71,Default,,0000,0000,0000,,这样就有了产物的生成热之和
Dialogue: 0,0:01:00.73,0:01:02.07,Default,,0000,0000,0000,,然后再减去
Dialogue: 0,0:01:02.09,0:01:03.94,Default,,0000,0000,0000,,反应物的生成热之和
Dialogue: 0,0:01:03.96,0:01:07.10,Default,,0000,0000,0000,,当然啦 O2的生成热是0
Dialogue: 0,0:01:07.11,0:01:08.51,Default,,0000,0000,0000,,所以式子里面没有这项
Dialogue: 0,0:01:08.52,0:01:11.91,Default,,0000,0000,0000,,算出来就是 -890.3kJ
Dialogue: 0,0:01:11.93,0:01:12.06,Default,,0000,0000,0000,,好啦
Dialogue: 0,0:01:12.07,0:01:14.95,Default,,0000,0000,0000,,这就说明 反应是放热的
Dialogue: 0,0:01:14.97,0:01:18.38,Default,,0000,0000,0000,,方程式这边的能量小于…
Dialogue: 0,0:01:18.40,0:01:19.63,Default,,0000,0000,0000,,你也可以这样想的…
Dialogue: 0,0:01:19.65,0:01:20.36,Default,,0000,0000,0000,,比那边的能量小
Dialogue: 0,0:01:20.37,0:01:22.65,Default,,0000,0000,0000,,所以必须释放能量才行
Dialogue: 0,0:01:22.67,0:01:25.43,Default,,0000,0000,0000,,可以在这里写 +e e代表能量
Dialogue: 0,0:01:25.44,0:01:25.92,Default,,0000,0000,0000,,我写上
Dialogue: 0,0:01:25.93,0:01:28.08,Default,,0000,0000,0000,,加上释放出来的能量
Dialogue: 0,0:01:28.10,0:01:29.72,Default,,0000,0000,0000,,这就是反应放热的原因啦
Dialogue: 0,0:01:29.74,0:01:31.96,Default,,0000,0000,0000,,但是问题是 反应是不是自发的呢？
Dialogue: 0,0:01:31.97,0:01:33.55,Default,,0000,0000,0000,,想要判断反应的自发性
Dialogue: 0,0:01:33.57,0:01:39.24,Default,,0000,0000,0000,,首先要算出ΔS
Dialogue: 0,0:01:39.26,0:01:41.38,Default,,0000,0000,0000,,为了计算ΔS的值呢
Dialogue: 0,0:01:41.40,0:01:43.19,Default,,0000,0000,0000,,我提前就查好了
Dialogue: 0,0:01:43.21,0:01:48.14,Default,,0000,0000,0000,,这里每种分子的标准摩尔熵
Dialogue: 0,0:01:48.16,0:01:49.61,Default,,0000,0000,0000,,比如说 标准…
Dialogue: 0,0:01:49.63,0:01:51.41,Default,,0000,0000,0000,,我换个颜色表示
Dialogue: 0,0:01:51.42,0:01:53.36,Default,,0000,0000,0000,,标准
Dialogue: 0,0:01:53.38,0:01:56.79,Default,,0000,0000,0000,,小小讲点拓展 这里没有Δ
Dialogue: 0,0:01:56.80,0:02:00.51,Default,,0000,0000,0000,,我擦了吧 还能补救
Dialogue: 0,0:02:00.53,0:02:02.85,Default,,0000,0000,0000,,标准
Dialogue: 0,0:02:02.87,0:02:05.24,Default,,0000,0000,0000,,这里画个圈里面带个横表示
Dialogue: 0,0:02:05.26,0:02:07.40,Default,,0000,0000,0000,,标准摩尔熵Sm
Dialogue: 0,0:02:07.41,0:02:10.85,Default,,0000,0000,0000,,“标准”指的是在298°K下
Dialogue: 0,0:02:10.86,0:02:12.66,Default,,0000,0000,0000,,实际不应该说“度开尔文”
Dialogue: 0,0:02:12.68,0:02:14.59,Default,,0000,0000,0000,,就是298K
Dialogue: 0,0:02:14.60,0:02:16.42,Default,,0000,0000,0000,,用开尔文K的时候
Dialogue: 0,0:02:16.44,0:02:17.45,Default,,0000,0000,0000,,不用说度°
Dialogue: 0,0:02:17.46,0:02:19.24,Default,,0000,0000,0000,,所以反应温度是289K
Dialogue: 0,0:02:19.26,0:02:20.65,Default,,0000,0000,0000,,也就是25°C
Dialogue: 0,0:02:20.66,0:02:22.10,Default,,0000,0000,0000,,相当于室温
Dialogue: 0,0:02:22.11,0:02:24.30,Default,,0000,0000,0000,,所以用289K作标准状态
Dialogue: 0,0:02:24.32,0:02:29.24,Default,,0000,0000,0000,,所以室温下 甲烷的标准摩尔熵
Dialogue: 0,0:02:29.26,0:02:31.03,Default,,0000,0000,0000,,就等于这个数
Dialogue: 0,0:02:37.81,0:02:40.38,Default,,0000,0000,0000,,所以如果有1mol的甲烷
Dialogue: 0,0:02:40.40,0:02:43.89,Default,,0000,0000,0000,,就有186J/K的熵
Dialogue: 0,0:02:43.90,0:02:46.13,Default,,0000,0000,0000,,如果有2mol的甲烷 就乘以2
Dialogue: 0,0:02:46.14,0:02:48.42,Default,,0000,0000,0000,,如果有3mol 就乘以3
Dialogue: 0,0:02:48.43,0:02:53.46,Default,,0000,0000,0000,,所以这个反应的总熵变
Dialogue: 0,0:02:53.47,0:02:58.02,Default,,0000,0000,0000,,就是产物标准熵之和
Dialogue: 0,0:02:58.04,0:03:00.69,Default,,0000,0000,0000,,减去反应物标准熵之和
Dialogue: 0,0:03:00.70,0:03:02.55,Default,,0000,0000,0000,,就跟算ΔHr差不多
Dialogue: 0,0:03:02.56,0:03:09.76,Default,,0000,0000,0000,,所以熵变就等于213.6 加上…
Dialogue: 0,0:03:09.77,0:03:12.39,Default,,0000,0000,0000,,产物里有2mol的水
Dialogue: 0,0:03:12.40,0:03:15.92,Default,,0000,0000,0000,,所以就是加上2乘以…
Dialogue: 0,0:03:15.94,0:03:17.85,Default,,0000,0000,0000,,就取70好了
Dialogue: 0,0:03:17.86,0:03:19.80,Default,,0000,0000,0000,,69.9 约等于70
Dialogue: 0,0:03:19.82,0:03:21.91,Default,,0000,0000,0000,,加上2×70
Dialogue: 0,0:03:21.92,0:03:23.79,Default,,0000,0000,0000,,然后再减去
Dialogue: 0,0:03:23.80,0:03:26.11,Default,,0000,0000,0000,,反应物的熵之和
Dialogue: 0,0:03:26.12,0:03:28.91,Default,,0000,0000,0000,,也就是方程式这边的这些
Dialogue: 0,0:03:28.92,0:03:31.77,Default,,0000,0000,0000,,1molCH4的熵
Dialogue: 0,0:03:31.78,0:03:42.86,Default,,0000,0000,0000,,等于186 加上2×205
Dialogue: 0,0:03:42.88,0:03:44.25,Default,,0000,0000,0000,,大概心算一下
Dialogue: 0,0:03:44.27,0:03:45.67,Default,,0000,0000,0000,,这个数非常接近这个数
Dialogue: 0,0:03:45.69,0:03:48.02,Default,,0000,0000,0000,,但是这个数比这个数大得多
Dialogue: 0,0:03:48.04,0:03:50.33,Default,,0000,0000,0000,,液态水的熵…
Dialogue: 0,0:03:50.35,0:03:51.99,Default,,0000,0000,0000,,这是液态水的熵
Dialogue: 0,0:03:52.00,0:03:54.65,Default,,0000,0000,0000,,它的熵远远小于氧气的熵
Dialogue: 0,0:03:54.67,0:03:55.76,Default,,0000,0000,0000,,这很合理呀
Dialogue: 0,0:03:55.77,0:03:58.57,Default,,0000,0000,0000,,因为液态水的微观状态数比氧气少得多
Dialogue: 0,0:03:58.58,0:04:02.37,Default,,0000,0000,0000,,液态水都沉在容器底了
Dialogue: 0,0:04:02.39,0:04:03.04,Default,,0000,0000,0000,,气体就不同
Dialogue: 0,0:04:03.05,0:04:04.67,Default,,0000,0000,0000,,气体能膨胀 随空间变换形状
Dialogue: 0,0:04:04.69,0:04:06.03,Default,,0000,0000,0000,,所以理所当然 气体的熵
Dialogue: 0,0:04:06.05,0:04:08.15,Default,,0000,0000,0000,,比液体的熵大的多
Dialogue: 0,0:04:08.17,0:04:09.26,Default,,0000,0000,0000,,简单心算
Dialogue: 0,0:04:09.27,0:04:12.28,Default,,0000,0000,0000,,就已经能看出来产物的熵
Dialogue: 0,0:04:12.30,0:04:14.02,Default,,0000,0000,0000,,比反应物的熵小
Dialogue: 0,0:04:14.03,0:04:15.46,Default,,0000,0000,0000,,所以熵变应该是负的
Dialogue: 0,0:04:15.48,0:04:19.43,Default,,0000,0000,0000,,不过我们还是确认一下
Dialogue: 0,0:04:19.44,0:04:28.54,Default,,0000,0000,0000,,这个是213.6加上…
Dialogue: 0,0:04:28.56,0:04:30.75,Default,,0000,0000,0000,,是加上140 对嘛？
Dialogue: 0,0:04:30.76,0:04:31.38,Default,,0000,0000,0000,,是2×70
Dialogue: 0,0:04:31.39,0:04:35.55,Default,,0000,0000,0000,,加上140 就等于353.6
Dialogue: 0,0:04:35.56,0:04:39.90,Default,,0000,0000,0000,,这部分等于353.6
Dialogue: 0,0:04:39.91,0:04:43.58,Default,,0000,0000,0000,,然后从这里减去…
Dialogue: 0,0:04:43.59,0:04:52.66,Default,,0000,0000,0000,,所以186 加上2×205
Dialogue: 0,0:04:52.67,0:04:54.43,Default,,0000,0000,0000,,就等于596
Dialogue: 0,0:04:54.44,0:04:57.17,Default,,0000,0000,0000,,所以就是减去596
Dialogue: 0,0:04:57.19,0:04:58.60,Default,,0000,0000,0000,,最后等于什么？
Dialogue: 0,0:04:58.62,0:05:06.43,Default,,0000,0000,0000,,-596 加上353.6
Dialogue: 0,0:05:06.44,0:05:10.52,Default,,0000,0000,0000,,等于-242.4
Dialogue: 0,0:05:10.53,0:05:17.61,Default,,0000,0000,0000,,所以它就等于-242.4J/K
Dialogue: 0,0:05:17.63,0:05:21.20,Default,,0000,0000,0000,,这就是ΔS 负的
Dialogue: 0,0:05:21.22,0:05:24.06,Default,,0000,0000,0000,,所以系统的熵减少了这么多
Dialogue: 0,0:05:24.08,0:05:25.98,Default,,0000,0000,0000,,你可能对熵的单位大小没有概念
Dialogue: 0,0:05:25.99,0:05:28.95,Default,,0000,0000,0000,,不过只要知道是某个大小就可以
Dialogue: 0,0:05:28.96,0:05:29.62,Default,,0000,0000,0000,,但是你可以说 喏
Dialogue: 0,0:05:29.63,0:05:30.83,Default,,0000,0000,0000,,反应之后系统更有序啦
Dialogue: 0,0:05:30.84,0:05:32.76,Default,,0000,0000,0000,,这很合理 因为开始是一大堆气体
Dialogue: 0,0:05:32.77,0:05:35.35,Default,,0000,0000,0000,,开始是3个单独的分子
Dialogue: 0,0:05:35.36,0:05:38.30,Default,,0000,0000,0000,,有1个甲烷 还有2个氧气
Dialogue: 0,0:05:38.31,0:05:40.08,Default,,0000,0000,0000,,后来还是3个分子
Dialogue: 0,0:05:40.10,0:05:42.39,Default,,0000,0000,0000,,但是这个水是液态的
Dialogue: 0,0:05:42.40,0:05:45.52,Default,,0000,0000,0000,,所以 反应后熵减小是有道理的
Dialogue: 0,0:05:45.53,0:05:48.57,Default,,0000,0000,0000,,尤其液态物质 它的微观状态数很少
Dialogue: 0,0:05:48.59,0:05:49.43,Default,,0000,0000,0000,,我们来判断一下
Dialogue: 0,0:05:49.45,0:05:51.21,Default,,0000,0000,0000,,这个反应是不是自发的
Dialogue: 0,0:05:51.22,0:05:57.51,Default,,0000,0000,0000,,ΔG等于ΔH…
Dialogue: 0,0:05:57.53,0:06:00.88,Default,,0000,0000,0000,,反应放热 所以就是-890
Dialogue: 0,0:06:00.90,0:06:02.54,Default,,0000,0000,0000,,我把小数省略掉了
Dialogue: 0,0:06:02.55,0:06:03.99,Default,,0000,0000,0000,,我们不用那么精确
Dialogue: 0,0:06:04.01,0:06:05.93,Default,,0000,0000,0000,,减去温度
Dialogue: 0,0:06:05.95,0:06:08.28,Default,,0000,0000,0000,,假设反应是在室温下进行的
Dialogue: 0,0:06:08.29,0:06:10.21,Default,,0000,0000,0000,,所以温度是298°K
Dialogue: 0,0:06:10.23,0:06:13.39,Default,,0000,0000,0000,,就是… 我应该说“298K”
Dialogue: 0,0:06:13.40,0:06:14.42,Default,,0000,0000,0000,,我要改掉坏习惯
Dialogue: 0,0:06:14.43,0:06:15.91,Default,,0000,0000,0000,,在用K表示温度的时候 不说“°”
Dialogue: 0,0:06:15.93,0:06:18.71,Default,,0000,0000,0000,,298K 也就是25°C
Dialogue: 0,0:06:18.73,0:06:22.10,Default,,0000,0000,0000,,再乘以熵变
Dialogue: 0,0:06:22.12,0:06:24.92,Default,,0000,0000,0000,,这项是负的
Dialogue: 0,0:06:24.94,0:06:27.46,Default,,0000,0000,0000,,你可能会说 好的 是-242
Dialogue: 0,0:06:27.47,0:06:28.54,Default,,0000,0000,0000,,直接把这个数放进去
Dialogue: 0,0:06:28.55,0:06:30.36,Default,,0000,0000,0000,,但是你要非常非常非常的小心
Dialogue: 0,0:06:30.37,0:06:33.04,Default,,0000,0000,0000,,它的单位是千焦kJ
Dialogue: 0,0:06:33.05,0:06:34.94,Default,,0000,0000,0000,,可是它的单位是焦耳J
Dialogue: 0,0:06:34.96,0:06:37.63,Default,,0000,0000,0000,,所以如果都以千焦做单位的话
Dialogue: 0,0:06:37.64,0:06:38.87,Default,,0000,0000,0000,,因为前面写了kJ
Dialogue: 0,0:06:38.89,0:06:40.48,Default,,0000,0000,0000,,我们把这个也换算成千焦吧
Dialogue: 0,0:06:40.50,0:06:46.99,Default,,0000,0000,0000,,所以它就是0.242kJ/K
Dialogue: 0,0:06:47.00,0:06:48.10,Default,,0000,0000,0000,,前面放个小数点
Dialogue: 0,0:06:48.11,0:06:50.11,Default,,0000,0000,0000,,这里的0.45擦掉
Dialogue: 0,0:06:50.12,0:06:51.89,Default,,0000,0000,0000,,单位是kJ/k
Dialogue: 0,0:06:51.91,0:06:55.51,Default,,0000,0000,0000,,所以吉布斯自由能变
Dialogue: 0,0:06:55.53,0:07:00.25,Default,,0000,0000,0000,,就是-890kJ 减去298…
Dialogue: 0,0:07:00.26,0:07:02.66,Default,,0000,0000,0000,,负负得正
Dialogue: 0,0:07:02.69,0:07:03.88,Default,,0000,0000,0000,,完全合理
Dialogue: 0,0:07:03.89,0:07:05.65,Default,,0000,0000,0000,,因为熵的这项
Dialogue: 0,0:07:05.66,0:07:08.39,Default,,0000,0000,0000,,会使吉布斯自由能变得更正
Dialogue: 0,0:07:08.41,0:07:09.41,Default,,0000,0000,0000,,因为
Dialogue: 0,0:07:09.43,0:07:12.08,Default,,0000,0000,0000,,我们想让ΔG<0
Dialogue: 0,0:07:12.09,0:07:14.07,Default,,0000,0000,0000,,但是ΔS>0会降低自发性
Dialogue: 0,0:07:14.09,0:07:18.84,Default,,0000,0000,0000,,现在我们来看这项能不能抵消ΔH
Dialogue: 0,0:07:18.85,0:07:20.59,Default,,0000,0000,0000,,也就是放热的影响
Dialogue: 0,0:07:20.61,0:07:21.67,Default,,0000,0000,0000,,目测好像是不行
Dialogue: 0,0:07:21.67,0:07:23.71,Default,,0000,0000,0000,,因为一个小数乘以它
Dialogue: 0,0:07:23.73,0:07:25.13,Default,,0000,0000,0000,,得到的数肯定更小
Dialogue: 0,0:07:25.15,0:07:26.72,Default,,0000,0000,0000,,我们算算看
Dialogue: 0,0:07:26.73,0:07:31.04,Default,,0000,0000,0000,,所以除以 1,2,3 3个0
Dialogue: 0,0:07:31.05,0:07:34.32,Default,,0000,0000,0000,,系统的熵变
Dialogue: 0,0:07:34.33,0:07:37.81,Default,,0000,0000,0000,,乘以298 这是系统的温度
Dialogue: 0,0:07:37.82,0:07:40.16,Default,,0000,0000,0000,,等于-72
Dialogue: 0,0:07:40.17,0:07:42.61,Default,,0000,0000,0000,,所以这项就等于…
Dialogue: 0,0:07:42.63,0:07:43.79,Default,,0000,0000,0000,,因为前面还有个减号…
Dialogue: 0,0:07:43.81,0:07:46.86,Default,,0000,0000,0000,,所以就是加上72.2
Dialogue: 0,0:07:46.87,0:07:50.01,Default,,0000,0000,0000,,所以这就是标准温度下的熵的项
Dialogue: 0,0:07:50.03,0:07:51.36,Default,,0000,0000,0000,,最后就等于它咯
Dialogue: 0,0:07:51.37,0:07:53.04,Default,,0000,0000,0000,,而这是焓项
Dialogue: 0,0:07:53.05,0:07:54.16,Default,,0000,0000,0000,,这样我们就能看出来
Dialogue: 0,0:07:54.18,0:07:57.02,Default,,0000,0000,0000,,焓变的绝对值
Dialogue: 0,0:07:57.04,0:07:59.04,Default,,0000,0000,0000,,比T×ΔS的绝对值
Dialogue: 0,0:07:59.05,0:08:00.37,Default,,0000,0000,0000,,大得多
Dialogue: 0,0:08:00.38,0:08:04.53,Default,,0000,0000,0000,,所以这项压倒性胜利了
Dialogue: 0,0:08:04.55,0:08:06.91,Default,,0000,0000,0000,,虽然反应是个熵减的反应
Dialogue: 0,0:08:06.92,0:08:09.11,Default,,0000,0000,0000,,但是反应放出的热量太多了
Dialogue: 0,0:08:09.13,0:08:10.93,Default,,0000,0000,0000,,所以反应仍然是自发
Dialogue: 0,0:08:10.95,0:08:12.89,Default,,0000,0000,0000,,这个数显然小于0
Dialogue: 0,0:08:12.91,0:08:17.34,Default,,0000,0000,0000,,所以这是个自发反应
Dialogue: 0,0:08:17.35,0:08:19.40,Default,,0000,0000,0000,,如你所见 这些吉布斯自由能的问题
Dialogue: 0,0:08:19.42,0:08:20.71,Default,,0000,0000,0000,,其实没那么难
Dialogue: 0,0:08:20.73,0:08:23.57,Default,,0000,0000,0000,,只要知道这几项的值就行啦
Dialogue: 0,0:08:23.58,0:08:27.13,Default,,0000,0000,0000,,这几项的值要么直接给出
Dialogue: 0,0:08:27.15,0:08:27.97,Default,,0000,0000,0000,,比如ΔH
Dialogue: 0,0:08:27.99,0:08:29.83,Default,,0000,0000,0000,,不过我们也知道怎么求出来
Dialogue: 0,0:08:29.85,0:08:31.24,Default,,0000,0000,0000,,只要查到产物的
Dialogue: 0,0:08:31.25,0:08:32.54,Default,,0000,0000,0000,,生成热
Dialogue: 0,0:08:32.55,0:08:34.64,Default,,0000,0000,0000,,再减去反应物的生成热
Dialogue: 0,0:08:34.65,0:08:37.77,Default,,0000,0000,0000,,当然还要各自乘以相应的化学计量数
Dialogue: 0,0:08:37.78,0:08:40.17,Default,,0000,0000,0000,,然后 用同样的方法
Dialogue: 0,0:08:40.18,0:08:41.01,Default,,0000,0000,0000,,算出熵变
Dialogue: 0,0:08:41.03,0:08:43.65,Default,,0000,0000,0000,,查到每种产物的标准摩尔熵
Dialogue: 0,0:08:43.67,0:08:46.00,Default,,0000,0000,0000,,分别乘以相应的化学计量数
Dialogue: 0,0:08:46.02,0:08:47.81,Default,,0000,0000,0000,,再减去反应物的总熵
Dialogue: 0,0:08:47.82,0:08:49.97,Default,,0000,0000,0000,,然后把数代入这个式子中
Dialogue: 0,0:08:49.99,0:08:51.98,Default,,0000,0000,0000,,最后就得到了吉布斯自由能变
Dialogue: 0,0:08:51.99,0:08:54.56,Default,,0000,0000,0000,,这个例子里 ΔG是负的
Dialogue: 0,0:08:54.57,0:08:56.17,Default,,0000,0000,0000,,现在 大家可以想象一下
Dialogue: 0,0:08:56.19,0:08:57.78,Default,,0000,0000,0000,,温度极高的情况
Dialogue: 0,0:08:57.80,0:09:00.20,Default,,0000,0000,0000,,比如太阳表面之类的
Dialogue: 0,0:09:00.22,0:09:04.00,Default,,0000,0000,0000,,温度就不是298K啦
Dialogue: 0,0:09:04.01,0:09:07.98,Default,,0000,0000,0000,,温度一下子变成了2000K或者4000K
Dialogue: 0,0:09:08.00,0:09:09.92,Default,,0000,0000,0000,,这时候就有意思啦
Dialogue: 0,0:09:09.94,0:09:11.43,Default,,0000,0000,0000,,比如说
Dialogue: 0,0:09:11.45,0:09:15.66,Default,,0000,0000,0000,,反应温度是40000K
Dialogue: 0,0:09:15.67,0:09:17.52,Default,,0000,0000,0000,,那么熵这一项
Dialogue: 0,0:09:17.54,0:09:19.87,Default,,0000,0000,0000,,也就是熵减 影响就可大啦
Dialogue: 0,0:09:19.89,0:09:22.30,Default,,0000,0000,0000,,所以正的这一项
Dialogue: 0,0:09:22.31,0:09:23.19,Default,,0000,0000,0000,,就抵消这一项
Dialogue: 0,0:09:23.21,0:09:25.65,Default,,0000,0000,0000,,所以在超高温下
Dialogue: 0,0:09:25.67,0:09:28.01,Default,,0000,0000,0000,,反应可能就无法自发进行啦
Dialogue: 0,0:09:28.02,0:09:29.11,Default,,0000,0000,0000,,换个角度
Dialogue: 0,0:09:29.12,0:09:34.23,Default,,0000,0000,0000,,一个反应放出热量…
Dialogue: 0,0:09:34.24,0:09:36.30,Default,,0000,0000,0000,,环境温度已经非常高
Dialogue: 0,0:09:36.31,0:09:38.18,Default,,0000,0000,0000,,分子的动能已经很大了的时候
Dialogue: 0,0:09:38.19,0:09:40.02,Default,,0000,0000,0000,,放出的热量就没什么影响了
Dialogue: 0,0:09:40.04,0:09:41.46,Default,,0000,0000,0000,,如果环境温度足够高
Dialogue: 0,0:09:41.48,0:09:43.89,Default,,0000,0000,0000,,这个反应就不是自发的了
Dialogue: 0,0:09:43.91,0:09:47.06,Default,,0000,0000,0000,,因为熵项会把焓抵消掉
Dialogue: 0,0:09:47.08,0:09:47.50,Default,,0000,0000,0000,,好啦
Dialogue: 0,0:09:47.52,0:09:49.02,Default,,0000,0000,0000,,我只是想带大家算一次
Dialogue: 0,0:09:49.04,0:09:51.35,Default,,0000,0000,0000,,就是想让大家知道 这没那么难
Dialogue: 0,0:09:51.37,0:09:53.01,Default,,0000,0000,0000,,这些数据都可以从网上查到
Dialogue: 0,0:09:53.02,0:09:54.00,Default,,0000,0000,0000,,然后就能判断出
Dialogue: 0,0:09:54.01,0:09:56.32,Default,,0000,0000,0000,,反应是否可以自发进行了