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In systems that are at a state of non-equilibrium there are, by contrast, net flows of matter or energy. If such changes can be triggered to occur in a system in which they are not already occurring, the system is said to be in a meta-stable equilibrium.

In systems that are at a state of non-equilibrium there are, by contrast, net flows of matter or energy. If such changes can be triggered to occur in a system in which they are not already occurring, the system is said to be in a meta-stable equilibrium.

Though not a widely named a "law," it is an axiom of thermodynamics that there exist states of thermodynamic equilibrium. The second law of thermodynamics states that when a body of material starts from an equilibrium state, in which, portions of it are held at different states by more or less permeable or impermeable partitions, and a thermodynamic operation removes or makes the partitions more permeable and it is isolated, then it spontaneously reaches its own, new state of internal thermodynamic equilibrium, and this is accompanied by an increase in the sum of the entropies of the portions.

Though not a widely named a "law," it is an axiom of thermodynamics that there exist states of thermodynamic equilibrium. The second law of thermodynamics states that when a body of material starts from an equilibrium state, in which, portions of it are held at different states by more or less permeable or impermeable partitions, and a thermodynamic operation removes or makes the partitions more permeable and it is isolated, then it spontaneously reaches its own, new state of internal thermodynamic equilibrium, and this is accompanied by an increase in the sum of the entropies of the portions.

虽然不是一个广泛命名的“定律” ，但它是一个热力学公理，即存在热力学平衡状态。热力学第二定律指出，当一个物质体从一个平衡状态开始，在这个状态中，它的一部分被或多或少渗透或不渗透的分区保持在不同的状态，热力学操作移除或使分区更具渗透性，它是孤立的，然后它自发地达到它自己的，内部热力学平衡的新状态，这是伴随着部分熵的总和的增加。

虽然不是一个广泛命名的“定律” ，但它是一个热力学'''<font color="#ff8000">公理 Axiom</font>'''，即存在热力学平衡状态。'''<font color="#ff8000">热力学第二定律 second law of thermodynamics</font>'''指出，当一个物质体从一个平衡状态开始，在这个状态中，它的一部分被或多或少渗透或不渗透的分区保持在不同的状态，热力学操作移除或使分区更具渗透性，它是孤立的，然后它自发地达到它自己的，内部热力学平衡的新状态，并伴随着部分'''<font color="#ff8000">熵 Entropy</font>'''的总和增加。

== Overview ==

== Overview ==

{{Thermodynamics|cTopic=[[Thermodynamic system|Systems]]}}

{{Thermodynamics|cTopic=[[Thermodynamic system|Systems]]}}

Classical thermodynamics deals with states of dynamic equilibrium. The state of a system at thermodynamic equilibrium is the one for which some thermodynamic potential is minimized, or for which the entropy (S) is maximized, for specified conditions. One such potential is the Helmholtz free energy (A), for a system with surroundings at controlled constant temperature and volume:

Classical thermodynamics deals with states of dynamic equilibrium. The state of a system at thermodynamic equilibrium is the one for which some thermodynamic potential is minimized, or for which the entropy (S) is maximized, for specified conditions. One such potential is the Helmholtz free energy (A), for a system with surroundings at controlled constant temperature and volume:

经典热力学研究动态平衡的状态。一个系统在热力学平衡的状态是一些热动力位能被最小化，或者熵(s)被最大化，对于特定的条件。一个这样的电位是亥姆霍兹自由能(a) ，用于一个周围环境温度和体积可控的系统:

经典热力学研究'''<font color="#ff8000">动态平衡 Dynamic Equilibrium</font>'''的状态。一个系统在热力学平衡的状态是一些'''<font color="#ff8000">热动力位能 Thermodynamic Potential</font>'''被最小化，或者'''<font color="#ff8000">熵 Entropy</font>'''(s)被最大化，对于特定的条件。一个这样的电位是'''<font color="#ff8000">亥姆霍兹自由能 Helmholtz Free Energy</font>'''(a) ，用于一个周围环境温度和体积可控的系统:

<math>A = U - TS</math>

<math>A = U - TS</math>

A = u-TS

A = U-TS

Another potential, the Gibbs free energy (G), is minimized at thermodynamic equilibrium in a system with surroundings at controlled constant temperature and pressure:

Another potential, the Gibbs free energy (G), is minimized at thermodynamic equilibrium in a system with surroundings at controlled constant temperature and pressure:

另一个潜在的吉布斯自由能，在恒定温度和压力下的系统中，在热力学平衡最小化:

另一个潜在的'''<font color="#ff8000">吉布斯自由能 Gibbs Free Energy</font>'''，在恒定温度和压力下的系统中，在热力学平衡最小化:

<math>G = U - TS + PV</math>

<math>G = U - TS + PV</math>

< math > g = u-TS + PV </math >  

<math>G = U - TS + PV</math>

where T denotes the absolute thermodynamic temperature, P the pressure, S the entropy, V the volume, and U the internal energy of the system.

where T denotes the absolute thermodynamic temperature, P the pressure, S the entropy, V the volume, and U the internal energy of the system.

其中 t 表示绝对热力学温度，p 表示压强，s 表示熵，v 表示体积，u 表示体系的内能。

其中 T 表示绝对热力学温度，P 表示压强，S 表示熵，V 表示体积，U 表示体系的内能。

== Conditions ==

== Conditions ==

* For a completely isolated system, ''S'' is maximum at thermodynamic equilibrium.

* For a completely isolated system, ''S'' is maximum at thermodynamic equilibrium. 对于一个完全孤立的系统，S是热力学平衡中最大值。

* For a system with controlled constant temperature and volume, ''A'' is minimum at thermodynamic equilibrium.

* For a system with controlled constant temperature and volume, ''A'' is minimum at thermodynamic equilibrium. 对于一个温度和体积可控的系统来说，A是热力学平衡的最小值。

* For a system with controlled constant temperature and pressure, ''G'' is minimum at thermodynamic equilibrium.

* For a system with controlled constant temperature and pressure, ''G'' is minimum at thermodynamic equilibrium. 对于一个恒温恒压的系统，G是热力学平衡的最小值。

实现各种类型的平衡的方法如下:

实现各种类型的平衡的方法如下:

*Two systems are in ''thermal equilibrium'' when their [[temperature]]s are the same.

*Two systems are in ''thermal equilibrium'' when their [[temperature]]s are the same. 当两个系统的'''<font color="#ff8000">温度 Temperature</font>'''相同时，它们就处于''热平衡状态''

*Two systems are in ''mechanical equilibrium'' when their [[pressure]]s are the same.

*Two systems are in ''mechanical equilibrium'' when their [[pressure]]s are the same. 当两个体系的'''<font color="#ff8000">压力 Pressure</font>'''相同时，它们就处于''力学平衡''

*Two systems are in ''diffusive equilibrium'' when their [[chemical potential]]s are the same.

*Two systems are in ''diffusive equilibrium'' when their [[chemical potential]]s are the same. 当两个题体系的'''<font color="#ff8000">化学势 Chemical Potential</font>'''相同时，它们就处于''扩散平衡''

*All [[forces]] are balanced and there is no significant external driving force.

*All [[forces]] are balanced and there is no significant external driving force.

 

==Relation of exchange equilibrium between systems==

==Relation of exchange equilibrium between systems==