Helmholtz and Gibbs Free Energies

Helmholtz Free Energy

赫尔姆霍茨自由能

Four quantities called "thermodynamic potentials" are useful in the chemical thermodynamics of reactions and non-cyclic processes. They are internal energy, the enthalpy, the Helmholtz free energy and the Gibbs free energy. The Helmholtz free energy F is defined by

四个称为“热力学势”的量在化学热力学中用于反应和非循环过程的分析。它们是内能、焓、亥姆霍兹自由能和吉布斯自由能。亥姆霍兹自由能 F 由以下公式定义：

The internal energy U might be thought of as the energy required to create a system in the absence of changes in temperature or volume. But if the system is created in an environment of temperature T, then some of the energy can be obtained by spontaneous heat transfer from the environment to the system. The amount of this spontaneous energy transfer is TS where S is the final entropy of the system. In that case, you don't have to put in as much energy. Note that if a more disordered (higher entropy) final state is created, less work is required to create the system. The Helmholtz free energy is then a measure of the amount of energy you have to put in to create a system once the spontaneous energy transfer to the sytem from the environment is accounted for.

内能U可以被理解为在没有温度或体积变化的情况下创造系统的所需能量。但如果系统是在温度为T的环境中创建的，那么可以通过环境自发地向系统传递热量来获得部分能量。这种自发的能量传递量为TS，其中S是系统的最终熵。在这种情况下，你不需要投入那么多能量。注意，如果创建了一个更无序（熵更高）的最终状态，那么创造系统的所需能量就会减少。因此，亥姆霍兹自由能是衡量在考虑了环境自发能量传递到系统之后，创造系统所需投入的能量的量。

The four thermodynamic potentials are related by offsets of the "energy from the environment" term TS and the "expansion work" term PV. A mnemonic diagram suggested by Schroeder can help you keep track of the relationships between the four thermodynamic potentials.

热力学四个势之间通过“来自环境的能量”项TS和“膨胀功”项PV的偏移而相关联。Schroeder提出的记忆图可以帮助你跟踪这四个热力学势之间的关系。

Gibbs Free Energy

吉布斯自由能

四个称为“热力学势”的量在化学热力学中用于反应和非循环过程的分析。它们是内能、焓、亥姆霍兹自由能和吉布斯自由能。吉布斯自由能G由以下公式定义：

The internal energy U might be thought of as the energy required to create a system in the absence of changes in temperature or volume. But as discussed in defining enthalpy, an additional amount of work PV must be done if the system is created from a very small volume in order to "create room" for the system. As discussed in defining the Helmholtz free energy, an environment at constant temperature T will contribute an amount TS to the system, reducing the overall investment necessary for creating the system. This net energy contribution for a system created in environment temperature T from a negligible initial volume is the Gibbs free energy.

内能U可以被理解为在没有温度或体积变化的情况下创造系统的能量。但正如定义焓时所讨论的，如果系统是从非常小的体积中创造出来的，为了‘为系统腾出空间’，还需要额外做功PV。正如定义亥姆霍兹自由能时所讨论的，一个温度恒定为T的环境会向系统贡献TS的能量，从而减少创造系统的总体能量投入。在从可忽略初始体积中创造一个在环境温度T下的系统的净能量贡献就是吉布斯自由能。

The change in Gibbs free energy, ΔG, in a reaction is a very useful parameter. It can be thought of as the maximum amount of work obtainable from a reaction. For example, in the oxidation of glucose, the change in Gibbs free energy is ΔG = 686 kcal = 2870 kJ. This reaction is the main energy reaction in living cells.

吉布斯自由能的变化ΔG是一个非常有用的参数。它可以被看作是反应所能提供的最大功。例如，在葡萄糖氧化反应中，吉布斯自由能的变化为ΔG = 686 kcal = 2870 kJ。这个反应是细胞中主要的能量反应。