20.2 标准导体

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  标准信封

  

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  How much energy is available?
  ::有多少能源可用?

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  As scientists explore energy supplies, geothermal sources look very appealing. The natural geysers that exist in some parts of the world could possibly be harnessed to provide power for many purposes. The change in energy content and the release of energy caused by steam condensing to can help fill some of our growing energy needs.
  ::当科学家探索能源供应时,地热资源看起来非常吸引人。 世界上某些地方存在的天然喷泉可以被利用来提供多种用途的电力。 蒸汽凝聚导致的能源含量变化和能源释放可以帮助满足我们日益增长的能源需求。

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  Standard Entropy
  ::标准信封

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  All molecular motion ceases at absolute zero (0 K). Therefore, the entropy of a pure crystalline substance at absolute zero is defined to be equal to zero. As the temperature of the substance increases, its entropy increases because of an increase in molecular motion. The absolute or standard entropy of substances can be measured. The symbol for entropy is  $\begin{array}{r}S\end{array}$ and the standard entropy of a substance is given by the symbol $\begin{array}{r}{S}^{\circ }\end{array}$ , indicating that the standard entropy is determined under standard conditions. The units for entropy are J/K • mol. Standard entropies for a few substances are shown in  Table :
  ::所有分子运动均以绝对0(0K)时停止。因此,在绝对零时,纯晶状物质的酶被定义为等于零。随着该物质的温度上升,其酶会因分子运动的增加而增加。可以测量物质的绝对或标准酶。该物质的绝对或标准酶的符号是S,物质的标准酶由符号S给定,表明标准酶是在标准条件下确定的。

  Standard Entropy Values at 25°C

  Substance	$\begin{array}{r}{S}^{\circ }(\text{J/K}\cdot \text{mol})\end{array}$
  H 2 (g)	131.0
  O 2 (g)	205.0
  H 2 O(l)	69.9
  H 2 O(g)	188.7
  C(graphite)	5.69
  C(diamond)	2.4

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  The knowledge of the absolute entropies of substances allows us to calculate the entropy change  $\begin{array}{r}(\mathrm{\Delta }{S}^{\circ })\end{array}$ for a reaction. For example, the entropy change for the vaporization of water can be found as follows:
  ::物质绝对分子的知识使我们可以计算反应的倍数变化(S)。例如,水蒸发的倍数变化如下:

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  $$\begin{array}{rl}\mathrm{\Delta }{S}^{\circ }& =S^{\circ }({\text{H}}_2\text{O}(g))-S^{\circ }({\text{H}}_2\text{O}(l))\\ & =188.7\text{J/K}\cdot \text{mol}-69.9\text{J/K}\cdot \text{mol}=118.8\text{J/K}\cdot \text{mol}\end{array}$$

  
  ::S(H2O(g))-S(H2O(l))=188.7 J/Kmol-69.9 J/Kmol=118.8 J/Kmol

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  The entropy change for the vaporization of water is positive because the state has higher entropy than the liquid state.
  ::水蒸发的酶变化是正的,因为国家具有高于液体的酶。

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  In general, the entropy change for a reaction can be determined if the standard entropies of each substance are known. The equation below can be applied.
  ::一般而言,如果了解每种物质的标准种性,就可以确定反应的酶变化。

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  $$\begin{array}{r}\mathrm{\Delta }{S}^{\circ }=\sum n{S}^{\circ }(\text{products})-\sum n{S}^{\circ }(\text{reactants})\end{array}$$

  
  :产品) (反应剂)

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  The standard entropy change is equal to the sum of all the standard entropies of the products minus the sum of all the standard entropies of the reactants . The symbol “ $\begin{array}{r}n\end{array}$ ” signifies that each entropy must first be multiplied by its coefficient in the balanced equation . The entropy change for the formation of liquid water from gaseous hydrogen and oxygen can be calculated using this equation:
  ::标准酶变化等于产品中所有标准活性成分的总和减去反应体中所有标准活性成分的总和。“n”符号表示,每个酶首先必须乘以平衡方程中系数。

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  $$\begin{array}{rl}& 2{\text{H}}_2(g)+{\text{O}}_2(g)\to 2{\text{H}}_2\text{O}(l)\\ & \mathrm{\Delta }{S}^{\circ }=2(69.9)-[2(131.0)+1(205.0)]=-327\text{J/K}\cdot \text{mol}\end{array}$$

  
  ::2H2(g) +O2(g) +O2(g)2H2O(l) (S) (269.9)-[2(131.0)+1(205.0)] 327 J/Kmol

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  The entropy change for this reaction is highly negative because three gaseous molecules are being converted into two liquid molecules. According to the drive towards higher entropy, the formation of water from hydrogen and oxygen is an unfavorable reaction. In this case, the reaction is highly exothermic and the drive towards a decrease in energy allows the reaction to occur.
  ::这种反应的酶变化非常消极,因为三个气体分子正被转化成两个液态分子。 根据朝向更高的酶的动力,氢和氧水的形成是一种不有利的反应。 在这种情况下,这种反应是高度发热的,而能量下降的动力使得反应得以发生。

   

   

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  Summary
  ::摘要

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  • Calculations of change in entropy using standard entropy are described.
    ::说明使用标准石英计算到的对石英变化的计算。

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  Review
  ::回顾

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  1. When is the entropy of any material at its lowest?
     ::任何材料的酶何时处于最低水平?
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  2. In the reaction involving the formation of water from hydrogen and oxygen, why is the entropy value negative?
     ::在涉及氢和氧水形成的反应中,为什么星体值为负值?
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  3. Why would diamond have a lower standard entropy value than graphite?
     ::钻石为什么比石墨有较低的标准石墨石英的石英值?