20.6 温度和免费能源

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• 选择节温度和自由能源

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  温度和自由能源

  

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  How is steel produced?
  ::钢是如何生产的?

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  Iron ore (Fe ₂ O ₃ ) and coke (an impure form of carbon) are heated together to make iron and carbon dioxide. The reaction is non-spontaneous at room temperature , but becomes spontaneous at temperature above 842 K. The iron can then be treated with small amounts of other materials to make a variety of steel products.
  ::铁矿石(Fe2O3)和焦炭(一种不纯的碳形式)一起加热,以制成铁和二氧化碳,在室温下反应不自发,但在温度高于842K时自发。 然后,铁可以用少量其他材料处理,生产各种钢制品。

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  Temperature and Free Energy
  ::温度和自由能源

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  Consider the in which calcium carbonate decomposes into calcium oxide and carbon dioxide . The production of CaO (called quicklime) has been an important reaction for centuries.
  ::碳酸钙分解成氧化钙和二氧化碳。 碳酸钙(caO)的生产(所谓的快速石灰)是几个世纪以来的重要反应。

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  $$\begin{align*}\text{CaCO}_3(s) \rightleftarrows \text{CaO}(s) +\text{CO}_2(g)\end{align*}$$
  ::CaCO3 +CaO +CO2(g)

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  The  $\begin{align*}\Delta H^\circ\end{align*}$ for the reaction is 177.8 kJ/mol, while the  $\begin{align*}\Delta S^\circ\end{align*}$ is 160.5 J/K • mol. The reaction is endothermic with an increase in entropy due to the production of a gas. We can first calculate the  $\begin{align*}\Delta G^\circ\end{align*}$ at 25°C in order to determine if the reaction is spontaneous at room temperature.
  ::反应为177.8 kJ/mol, 反应为160.5 J/K / mol。 反应为终端热, 由于气体的产生, 酶会增加。 我们可以首先计算25°C 的QG , 以确定在室温下反应是否自发 。

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  $$\begin{align*}\Delta G^\circ=\Delta H^\circ -T \Delta S^\circ=177.8 \ \text{kJ}/ \text{mol} - 298 \ K (0.1605 \ \text{kJ} / \text{K} \cdot \text{mol})=130.0 \ \text{kJ} / \text{mol}\end{align*}$$
  ::GHTS177.8 kJ/mol-298 K(0.1605 kJ/Kmol)=130.0 kJ/mol

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  Since the  $\begin{align*}\Delta G^\circ\end{align*}$ is a large positive quantity, the reaction strongly favors the reactants and very little products would be formed. In order to determine a temperature at which  $\begin{align*}\Delta G^\circ\end{align*}$ will become negative, we can first solve the equation for the temperature when  $\begin{align*}\Delta G^\circ\end{align*}$ is equal to zero.
  ::由于QG是一个很大的正数,反应强烈地有利于反应者,并且会形成非常小的产品。 为了确定一个温度,当QG等于零时,我们首先可以解答温度的方程式。

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  $$\begin{align*}0 &=\Delta H^\circ - T \Delta S^\circ \\ T &=\frac{\Delta H^\circ}{\Delta S^\circ}= \frac{177.8 \ \text{kJ} / \text{mol}}{0.1605 \ \text{kJ} / \text{K} \cdot \text{mol}}=1108 \text{ K}=835^\circ \text{ C}\end{align*}$$
  ::0HTSTHS177.8 kJ/mol0.1605 kJ/Kmol=1108 K=835C

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  So at any temperature higher than 835°C, the value of  $\begin{align*}\Delta G^\circ\end{align*}$ will be negative and the will be spontaneous.
  ::因此,在高于835°C的任何温度下, G的值将是负的, 并且是自发的。

  

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  This lime kiln in Cornwall was used to produce quicklime (calcium oxide), an important ingredient in mortar and cement.
  ::康沃尔的这种石灰窑用于生产活性石灰(氧化钙),这是迫击炮和水泥的重要成分。

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  Recall that the assumption that  $\begin{align*}\Delta H^\circ\end{align*}$ and  $\begin{align*}\Delta S^\circ\end{align*}$ are independent of temperature means that the temperature at which the sign of  $\begin{align*}\Delta G^\circ\end{align*}$ switches from being positive to negative (835°C) is an approximation. It is also important to point out that one should not assume that absolutely no products are formed below 835°C and that at that temperature decomposition suddenly begins. Rather, at lower temperatures, the amount of products formed is simply not great enough to say that the products are favored. When this reaction is performed, the amount of products can be detected by monitoring the pressure of the CO ₂ gas that is produced. Above about 700°C, measurable amounts of CO ₂ are produced. The pressure of CO ₂ at equilibrium gradually increases with increasing temperature. Above 835°C, the pressure of CO ₂ at equilibrium begins to exceed 1 atm, the standard-state pressure. This is an indication that the products of the reaction are now favored above that temperature. When quicklime is manufactured, the CO ₂ is constantly removed from the reaction as it is produced. This causes the reaction to be driven towards the products according to LeChâtelier’s principle.
  ::回顾“H”和“S”与温度无关的假设意味着“G”开关的信号从正向负的温度(835°C)是一个近似值。同样重要的是,人们不应假设绝对没有产品形成在835°C之下,在温度分解时突然开始。相反,在较低的温度下,所形成的产品数量不足以表示产品是有利的。当进行这种反应时,可以通过监测产生的二氧化碳气体的压力来检测产品的数量。在700°C以上,可测量的CO2数量是生产的。平衡的CO2压力随着温度的上升而逐渐增加。高于835°C,平衡的CO2压力开始超过1 小时,标准状态压力。这表明反应的产品现在比温度高。当制造快速石灰时,CO2会不断从产生的反应中去除。这导致按照Lechâtirier的原则向产品推进的反应。

   

   

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  Summary
  ::摘要

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  • The influence of temperature on free energy is described.
    ::介绍了温度对自由能源的影响。

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  Review
  ::回顾

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  1. If you increased the pressure of CO ₂ in the quicklime reaction, what would happen to the equilibrium?
     ::如果你在速石反应中增加二氧化碳的压力, 平衡会怎样呢?
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  2. Why do we calculate the situation where  $\begin{align*}\Delta G\end{align*}$ is zero?
     ::为何我们计算G为零的情况?
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  3. At temperatures below 835°C, is any product formed?
     ::在835摄氏度以下的温度下,有没有形成任何产品?