Absolute Entropy and Entropy Change · 绝对熵与熵变
| English | 中文 | Pinyin · 拼音 |
|---|---|---|
| standard molar entropy/ˈstændəd ˈməʊlə ˈentrəpi/ | 标准摩尔熵 | biāo zhǔn mó ěr shāng |
Adding up the disorder
- Every substance has its own tabulated disorder value.
- Add up products and subtract reactants, just like enthalpy.
- The result tells you if a reaction spreads out or tightens up.
- You can even predict the sign at a glance.
把无序加起来
- 每种物质都有自己列成表的无序值。
- 把产物加起来、减去反应物,就像焓一样。
- 结果告诉你反应是散开还是收紧。
- 你甚至能一眼预测符号。
Standard molar entropy
- Each substance has a standard molar entropy 标准摩尔熵 $S°$.
- Unlike formation enthalpy, even elements have a nonzero $S°$.
- Gases have large values; solids have small ones.
标准摩尔熵
- 每种物质都有一个标准摩尔熵 $S°$。
- 与生成焓不同,连元素也有非零的 $S°$。
- 气体值很大;固体值很小。
An element in its standard state has a standard entropy of zero. · 处于标准状态的元素的标准熵为零。
Unlike formation enthalpy, every substance has a positive $S°$. · 与生成焓不同，每种物质都有正值的 $S°$。
Products minus reactants
- $\Delta S_{rxn} = \sum S°(\text{products}) - \sum S°(\text{reactants})$.
- A positive result means the reaction becomes more disordered.
- Multiply each entropy by its coefficient first.
产物减反应物
- $\Delta S_{rxn} = \sum S°(\text{products}) - \sum S°(\text{reactants})$。
- 结果为正意味着反应变得更无序。
- 先把每个熵乘以它的系数。
A reaction's entropy change is... · 反应的熵变是...
$\Delta S = \sum S°(\text{products}) - \sum S°(\text{reactants})$.
You multiply each standard entropy by its coefficient before summing. · 求和前需将每个标准熵乘以其系数。
Coefficients scale the amount of each substance. · 系数按比例缩放每种物质的量。
Predicting the sign
- More gas moles on the product side give a positive $\Delta S$.
- Fewer gas moles give a negative $\Delta S$.
- A quick glance at the gas count often settles it.
预测符号
- 产物一侧气体摩尔数更多,给出正的 $\Delta S$。
- 气体摩尔数更少,给出负的 $\Delta S$。
- 快速瞥一眼气体数目常能定夺。
Sign of ΔS · ΔS 的符号
Sort each reaction by the sign of its entropy change, using the change in moles of gas. · 根据气体摩尔数的变化，按熵变的符号对每个反应进行分类。
A reaction that consumes gas and forms only solids has $\Delta S$ that is... · 消耗气体并只生成固体的反应，其 $\Delta S$ 是...
Losing gas moles lowers the disorder, so $\Delta S < 0$. · 失去气体摩尔数会降低无序度，所以 $\Delta S < 0$。
Which substance typically has the largest standard entropy? · 哪种物质通常具有最大的标准熵？
Gases are the most spread out, so they have the highest $S°$. · 气体最分散，因此它们具有最高的 $S°$。
Forming more moles of gas gives a ____ entropy change. · 形成更多摩尔的气体会导致 ____ 熵变。
More gas means more disorder, so $\Delta S > 0$. · 更多的气体意味着更多的无序，所以 $\Delta S > 0$。
A reaction turns 2 gas molecules into 1. What is the sign of $\Delta S$?
- Fewer gas molecules means less disorder.
- So $\Delta S$ is negative.
一个反应把 2 个气体分子变成 1 个。$\Delta S$ 的符号是什么?
- 气体分子更少意味着更无序程度更低。
- 所以 $\Delta S$ 为负。
Unlike $\Delta H_f$, elements do not have zero standard entropy -- every substance has a positive $S°$. Use products minus reactants, each times its coefficient. And you can usually predict the sign from the change in the number of gas moles.
与 $\Delta H_f$ 不同,元素没有零标准熵——每种物质都有正的 $S°$。用产物减反应物,各乘以它的系数。而且你通常能从气体摩尔数的变化预测符号。
Every substance has a positive standard molar entropy $S°$ (even elements). A reaction's entropy change is $\Delta S_{rxn} = \sum S°(\text{products}) - \sum S°(\text{reactants})$, scaled by coefficients. Its sign usually follows the change in gas moles: more gas gives positive $\Delta S$.
每种物质都有正的标准摩尔熵 $S°$(连元素也有)。反应的熵变是 $\Delta S_{rxn} = \sum S°(\text{products}) - \sum S°(\text{reactants})$,按系数缩放。它的符号通常跟随气体摩尔数的变化:气体更多给出正的 $\Delta S$。