免费能源

All aboard!
::全体上车!

The steam engine pictured above is slowly going out of style, but is still a picturesque part of the modern railroad. The water in a boiler is heated by a fire (usually fueled by coal) and turned to steam. This steam then pushes the pistons that drive the wheels of the train. It is the pressure created by the steam which allows work to be done in moving the train.
::上面所描绘的蒸汽引擎正在慢慢地失去风格,但仍然是现代铁路中一个光滑的部分。锅炉中的水被火(通常由煤炭加热)加热,变成蒸汽。这种蒸汽会推动驱动火车轮的活塞。正是蒸汽产生的压力使得在移动火车的过程中能够进行工作。

Free Energy
::免费能源

Many and physical processes release energy that can be used to do other things. When the fuel in a car is burned, some of the released energy is used to power the vehicle. Free energy is energy that is available to do work. Spontaneous reactions release free energy as they proceed. Recall that the determining factors for spontaneity of a reaction are the and entropy changes that occur for the system . The free energy change of a reaction is a mathematical combination of the enthalpy change and the entropy change.
::许多过程和物理过程释放出可以用来做其他事情的能量。当汽车的燃料被燃烧时,一些释放的能量被用来为汽车提供动力。免费能源是可用于工作的能源。自发反应在进行过程中释放出自由的能量。回顾反应自发性的决定因素是系统发生的和催化变化。反应的自由能量变化是蚂蚁变化和酶变化的数学组合。

The symbol for free energy is $\begin{array}{r}G\end{array}$ , in honor of American scientist Josiah Gibbs (1839-1903), who made many contributions to thermodynamics. The change in Gibbs free energy is equal to the change in enthalpy minus the mathematical product of the change in entropy multiplied by the Kelvin temperature . Each thermodynamic quantity in the equation is for substances in their standard states. The usual units for $\begin{array}{r}\mathrm{\Delta }H\end{array}$ is kJ/mol, while $\begin{array}{r}\mathrm{\Delta }S\end{array}$ is often reported in J/K • mol. It is necessary to change the units for $\begin{array}{r}\mathrm{\Delta }S\end{array}$ to kJ/K • mol, so that the calculation of $\begin{array}{r}\mathrm{\Delta }G\end{array}$ is in kJ/mol.
::免费能源的象征是G,这是美国科学家Josiah Gibbs的荣誉(1839-1903年),他为热力学做出了许多贡献。Gibbs的免费能源变化等于英特罗比变化的正弦和数学产品除以凯尔文温度乘以英特罗比的变换。方程式中的每个热力数量都针对其标准状态的物质。 H的通常单位是 kJ/mol, 而S通常在 J/K / mol 中报告。 有必要将 S 的单位改为 kJ/K / 摩尔, 以便计算 G 的单位在 kJ/ 摩尔 中 。

A spontaneous reaction is one that releases free energy, and so the sign of $\begin{array}{r}\mathrm{\Delta }G\end{array}$ must be negative. Since both $\begin{array}{r}\mathrm{\Delta }H\end{array}$ and $\begin{array}{r}\mathrm{\Delta }S\end{array}$ can be either positive or negative, depending on the characteristics of the particular reaction, there are four different general outcomes for $\begin{array}{r}\mathrm{\Delta }G\end{array}$ and these are outlined in  Table :
::一种自发反应是一种释放自由能量的反应,因此“G”的标志必须是负的。由于“H”和“S”都可以是正的,也可以是负的,取决于特定反应的特点,“G”有四种不同的一般结果,这些结果见表:

Keep in mind that the temperature in the Gibbs free energy equation is the Kelvin temperature and so can only be positive. When $\begin{array}{r}\mathrm{\Delta }H\end{array}$ is negative and $\begin{array}{r}\mathrm{\Delta }S\end{array}$ is positive, the sign of $\begin{array}{r}\mathrm{\Delta }G\end{array}$ will always be negative, and the reaction will be spontaneous at all temperatures. This corresponds to both driving forces being in favor of product formation. When $\begin{array}{r}\mathrm{\Delta }H\end{array}$ is positive and $\begin{array}{r}\mathrm{\Delta }S\end{array}$ is negative, the sign of $\begin{array}{r}\mathrm{\Delta }G\end{array}$ will always be positive, and the reaction can never be spontaneous. This corresponds to both driving forces working against product formation.
::记住 Gibbs 免费能源方程式中的温度是 Kelvin 温度, 因而只能是正数。 当 ++H 是负数, 和 ++S 是正数时, Q+G 的信号总是负数, 反应会在所有温度下都是自发的。 这与两种驱动力都赞成产品形成相对应。 当 +H 是正数, 和 ++S 是负数, QG 的信号总是正数, 反应永远不会是自发的。 这与反对产品形成的两个驱动力相对应。

When one driving force favors the reaction, but the other does not, it is the temperature that determines the sign of $\begin{array}{r}\mathrm{\Delta }G\end{array}$ . Consider first an endothermic reaction (positive $\begin{array}{r}\mathrm{\Delta }H\end{array}$ ) that also displays an increase in entropy (positive $\begin{array}{r}\mathrm{\Delta }S\end{array}$ ). It is the entropy term that favors the reaction. Therefore, as the temperature increases, the $\begin{array}{r}T\mathrm{\Delta }S\end{array}$ term in the Gibbs free energy equation will begin to predominate and $\begin{array}{r}\mathrm{\Delta }G\end{array}$ will become negative. A common example of a process which falls into this category is the of ice. At a relatively low temperature (below 273 K), the melting is not spontaneous because the positive $\begin{array}{r}\mathrm{\Delta }H\end{array}$ term “outweighs” the $\begin{array}{r}T\mathrm{\Delta }S\end{array}$ term. When the temperature rises above 273 K, the process becomes spontaneous because the larger $\begin{array}{r}T\end{array}$ value has tipped the sign of $\begin{array}{r}\mathrm{\Delta }G\end{array}$ over to being negative.
::当一个驱动力赞成反应,而另一个驱动力则不赞成反应时,是温度决定了“G.”的标志。首先考虑一种最终热反应(正 H),这种反应也显示过激(正 S) 的增加。这是有利于反应的催化词。因此,随着温度的上升,Gibbs自由能源方程式中的TS术语将开始占上风,而“G”类中的TS术语将变成负值。属于这一类别的过程的一个常见例子是冰。在相对较低的温度(低于273K)下,融化不是自发的,因为正的“H”词“出界”是TS。当温度上升超过273K时,这一过程就会自动发生,因为更大的T值使“G”的信号变为负值。

When the reaction is exothermic (negative $\begin{array}{r}\mathrm{\Delta }H\end{array}$ ) but undergoes a decrease in entropy (negative $\begin{array}{r}\mathrm{\Delta }S\end{array}$ ), it is the enthalpy term that favors the reaction. In this case, a spontaneous reaction is dependent upon the $\begin{array}{r}T\mathrm{\Delta }S\end{array}$ term being small relative to the $\begin{array}{r}\mathrm{\Delta }H\end{array}$ term, so that $\begin{array}{r}\mathrm{\Delta }G\end{array}$ is negative. The of water is an example of this type of process. It is spontaneous only at a relatively low temperature. Above 273 K, the larger $\begin{array}{r}T\mathrm{\Delta }S\end{array}$ value causes the sign of $\begin{array}{r}\mathrm{\Delta }G\end{array}$ to be positive, and freezing does not occur. 
::当反应是异热反应(阴性 H) , 但却是过低的 entropy (负性 S) 反应时, 偏好反应的是Py( S) 。 在这种情况下, 自发反应取决于TS 值相对于 S 值小于 H 值, 所以QG 是负的。 水是这种过程的一个例子。 水只在相对较低的温度下自发发生。 超过 273 K, 较大的 S 值使 G 表示是正的, 没有冻结发生 。

Summary
::摘要

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• Free energy is energy that is available to do work.
  ::免费能源是可供工作使用的能源。
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• Relationships between enthalpy, entropy, and free energy are described.
  ::描述enthalpy、entropy和免费能源之间的关系。

Review
::回顾

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1. What do spontaneous reactions do?
   ::自发反应会做什么?
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2. What are the units for $\begin{array}{r}\mathrm{\Delta }H\end{array}$ ?
   ::HH的单位是什么?
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3. What are the units for $\begin{array}{r}\mathrm{\Delta }S\end{array}$ ?
   ::什么是单位为QS?

Explore More
::探索更多

Use the resource below to answer the questions that follow.
::利用以下资源回答以下问题。

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1. What is another term for free energy?
   ::另一个免费能源的术语是什么?
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2. What happens to the total energy when the ball rolls down the slide?
   ::当球滚下幻灯片时,总能量会怎么样?
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3. How does $\begin{array}{r}H\end{array}$ change in a spontaneous reaction?
   ::H是如何改变自发反应的?
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4. How does $\begin{array}{r}S\end{array}$ change in a spontaneous reaction?
   ::S如何改变自发反应?