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{{Thermodynamics|cTopic=Laws}}

{{Thermodynamics|cTopic=Laws}}

The laws of thermodynamics define physical quantities, such as temperature, energy, and entropy, that characterize thermodynamic systems at thermodynamic equilibrium. The laws describe the relationships between these quantities, and form a basis of precluding the possibility of certain phenomena, such as perpetual motion. In addition to their use in thermodynamics, they are important fundamental laws of physics in general, and are applicable in other natural sciences.

The laws of thermodynamics define physical quantities, such as temperature, energy, and entropy, that characterize thermodynamic systems at thermodynamic equilibrium. The laws describe the relationships between these quantities, and form a basis of precluding the possibility of certain phenomena, such as perpetual motion. In addition to their use in thermodynamics, they are important fundamental laws of physics in general, and are applicable in other natural sciences.

 

 

Thermodynamics has traditionally recognized three fundamental laws, simply named by an ordinal identification, the first law, the second law, and the third law.. In addition, after the first three laws were established, it was recognized that another law, more fundamental to all three, could be stated, which was named the zeroth law.

Thermodynamics has traditionally recognized three fundamental laws, simply named by an ordinal identification, the first law, the second law, and the third law.. In addition, after the first three laws were established, it was recognized that another law, more fundamental to all three, could be stated, which was named the zeroth law.

The zeroth law of thermodynamics defines thermal equilibrium and forms a basis for the definition of temperature:  If two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other.

The zeroth law of thermodynamics defines thermal equilibrium and forms a basis for the definition of temperature:  If two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other.

The first law of thermodynamics: When energy passes, as work, as heat, or with matter, into or out of a system, the system's internal energy changes in accord with the law of conservation of energy. Equivalently, perpetual motion machines of the first kind (machines that produce work with no energy input) are impossible.

The first law of thermodynamics: When energy passes, as work, as heat, or with matter, into or out of a system, the system's internal energy changes in accord with the law of conservation of energy. Equivalently, perpetual motion machines of the first kind (machines that produce work with no energy input) are impossible.

能量守恒定律: 当能量以功、热或物质的形式进入或离开一个系统时，该系统的内部能量按照能量守恒定律发生变化。同样地，第一类永动机机器(不需要能量输入就能工作的机器)是不可能的。

热力学第一定律:当能量以功、热或物质的形式进入或离开一个系统时，系统的内能根据能量守恒定律发生变化。同样地，第一类永动机机器(不需要能量输入就能工作的机器)是不可能造成的。

The second law of thermodynamics: In a natural thermodynamic process, the sum of the entropies of the interacting thermodynamic systems increases. Equivalently, perpetual motion machines of the second kind (machines that spontaneously convert thermal energy into mechanical work) are impossible.

The second law of thermodynamics: In a natural thermodynamic process, the sum of the entropies of the interacting thermodynamic systems increases. Equivalently, perpetual motion machines of the second kind (machines that spontaneously convert thermal energy into mechanical work) are impossible.

热力学第二定律: 在自然热力学过程中，相互作用的热力学系统的熵之和增加。同样地，第二类永动机机器(自发地将热能转化为机械功的机器)是不可能的。

热力学第二定律:在自然热力学过程中，相互作用的热力学系统的熵的总和增加。同样地，第二类永动机(自发地把热能转化为机械功的机器)是不可能制造出的。

The third law of thermodynamics: The entropy of a system approaches a constant value as the temperature approaches absolute zero.  With the exception of non-crystalline solids (glasses) the entropy of a system at absolute zero is typically close to zero.

The third law of thermodynamics: The entropy of a system approaches a constant value as the temperature approaches absolute zero.  With the exception of non-crystalline solids (glasses) the entropy of a system at absolute zero is typically close to zero.

热力学第三定律: 当温度接近绝对零度时，系统的熵接近一个常数值。除了非晶体固体(玻璃)以外，系统在绝对零度时的熵通常接近于零。

热力学第三定律:当温度趋于绝对零度时，系统的熵趋于一个定值。除非晶固体(玻璃)外，系统在绝对零度时的熵通常接近于零。

Additional laws have been suggested, but none of them achieved the generality of the four accepted laws, and are not discussed in standard textbooks.

Additional laws have been suggested, but none of them achieved the generality of the four accepted laws, and are not discussed in standard textbooks.

 

The zeroth law of thermodynamics may be stated in the following form:

The zeroth law of thermodynamics may be stated in the following form:

The law is intended to allow the existence of an empirical parameter, the temperature, as a property of a system such that systems in thermal equilibrium with each other have the same temperature. The law as stated here is compatible with the use of a particular physical body, for example a mass of gas, to match temperatures of other bodies, but does not justify regarding temperature as a quantity that can be measured on a scale of real numbers.

The law is intended to allow the existence of an empirical parameter, the temperature, as a property of a system such that systems in thermal equilibrium with each other have the same temperature. The law as stated here is compatible with the use of a particular physical body, for example a mass of gas, to match temperatures of other bodies, but does not justify regarding temperature as a quantity that can be measured on a scale of real numbers.

Though this version of the law is one of the most commonly stated versions, it is only one of a diversity of statements that are labeled as "the zeroth law" by competent writers. Some statements go further so as to supply the important physical fact that temperature is one-dimensional and  that one can conceptually arrange bodies in real number sequence from colder to hotter. Perhaps there exists no unique "best possible statement" of the "zeroth law", because there is in the literature a range of formulations of the principles of thermodynamics, each of which call for their respectively appropriate versions of the law.

Though this version of the law is one of the most commonly stated versions, it is only one of a diversity of statements that are labeled as "the zeroth law" by competent writers. Some statements go further so as to supply the important physical fact that temperature is one-dimensional and  that one can conceptually arrange bodies in real number sequence from colder to hotter. Perhaps there exists no unique "best possible statement" of the "zeroth law", because there is in the literature a range of formulations of the principles of thermodynamics, each of which call for their respectively appropriate versions of the law.

Although these concepts of temperature and of thermal equilibrium are fundamental to thermodynamics and were clearly stated in the nineteenth century, the desire to explicitly number the above law was not widely felt until Fowler and Guggenheim did so in the 1930s, long after the first, second, and third law were already widely understood and recognized.  Hence it was numbered the zeroth law. The importance of the law as a foundation to the earlier laws is that it allows the definition of temperature in a non-circular way without reference to entropy, its conjugate variable. Such a temperature definition is said to be 'empirical'.

Although these concepts of temperature and of thermal equilibrium are fundamental to thermodynamics and were clearly stated in the nineteenth century, the desire to explicitly number the above law was not widely felt until Fowler and Guggenheim did so in the 1930s, long after the first, second, and third law were already widely understood and recognized.  Hence it was numbered the zeroth law. The importance of the law as a foundation to the earlier laws is that it allows the definition of temperature in a non-circular way without reference to entropy, its conjugate variable. Such a temperature definition is said to be 'empirical'.

The first law of thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic systems.

The first law of thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic systems.

The law of conservation of energy states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but can be neither created nor destroyed.

The law of conservation of energy states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but can be neither created nor destroyed.

能量守恒定律指出，孤立系统的总能量是恒定的; 能量可以从一种形式转化为另一种形式，但既不能被创造也不能被破坏。

能量守恒定律指出，一个孤立系统的总能量是恒定的;能量可以从一种形式转化为另一种形式，但能量既不会凭空产生也不会凭空消失。

For a thermodynamic process without transfer of matter, the first law is often formulated

For a thermodynamic process without transfer of matter, the first law is often formulated

where  denotes the change in the internal energy  of a closed system,  denotes the quantity of energy supplied to the system as heat, and  denotes the amount of thermodynamic work (expressed here with a negative sign) done by the system on its surroundings. (An alternate sign convention not used in this article is to define  as the work done on the system.)  

where  denotes the change in the internal energy  of a closed system,  denotes the quantity of energy supplied to the system as heat, and  denotes the amount of thermodynamic work (expressed here with a negative sign) done by the system on its surroundings. (An alternate sign convention not used in this article is to define  as the work done on the system.)  

其中表示一个封闭系统内部能量的变化，表示作为热量提供给该系统的能量的数量，并表示该系统在其周围所做的热力学功的数量(在这里用负号表示)。(本文中没有使用的另一个符号约定是定义在系统上完成的工作。)

其中{{math|Δ''U''_system}}表示一个封闭系统内部能量的变化，{{math|''Q''}} 表示外界对系统传递的热量，{{math|''W''}}表示该系统对周围环境所做的热力学功(在这里用负号表示)。(本文中没有使用的另一个符号约定是定义对系统所做的功。

In the case of a two-stage thermodynamic cycle of a closed system, which returns to its original state, the heat  supplied to the system in one stage of the cycle, minus the heat  removed from it in the other stage, plus the thermodynamic work added to the system, , equals the thermodynamic work that leaves the system .

In the case of a two-stage thermodynamic cycle of a closed system, which returns to its original state, the heat  supplied to the system in one stage of the cycle, minus the heat  removed from it in the other stage, plus the thermodynamic work added to the system, , equals the thermodynamic work that leaves the system .

For the particular case of a thermally isolated system (adiabatically isolated), the change of the internal energy of an adiabatically isolated system can only be the result of the work added to the system, because the adiabatic assumption is:  0}}.

For the particular case of a thermally isolated system (adiabatically isolated), the change of the internal energy of an adiabatically isolated system can only be the result of the work added to the system, because the adiabatic assumption is:  0}}.

对于绝热孤立热孤立系统的特殊情况，绝热孤立系统内能的变化只能是系统所做功的结果，因为绝热假设是: 0}。

对于绝热系统（绝热隔离）的特殊情况，绝热隔离系统内能的变化只能是系统做功的结果，因为绝热假设是: 0}。

For  processes that include transfer of matter, a further statement is needed: 'With due account of the respective fiducial reference states of the systems, when two systems, which may be of different chemical compositions, initially separated only by an impermeable wall, and otherwise isolated, are combined into a new system by the thermodynamic operation of removal of the wall, then

For  processes that include transfer of matter, a further statement is needed: 'With due account of the respective fiducial reference states of the systems, when two systems, which may be of different chemical compositions, initially separated only by an impermeable wall, and otherwise isolated, are combined into a new system by the thermodynamic operation of removal of the wall, then

对于包括物质转移的过程，需要进一步的陈述: ‘在适当考虑了各个系统的基准参考状态后，当两个系统---- 它们可能是不同的化学成分，最初只是被不透水的墙隔开，或者是被隔离---- 通过移除热力学操作结合成一个新的系统，那么

对于包括物质转移的过程，还需要进一步的说明: ‘在充分考虑了各个系统的基准参考状态后，当两个系统---- '''<font color="#32CD32">它们可能由不同的化学成分组成，最初只是被防渗墙隔开，或者是被隔离---- 通过移除墙体的热力学操作结合成一个新系统</font>'''，那么

where  denotes the internal energy  of the combined system, and  and  denote the internal energies of the respective separated systems.'

where  denotes the internal energy  of the combined system, and  and  denote the internal energies of the respective separated systems.'

This states that energy can be neither created nor destroyed. However, energy can change forms, and energy can flow from one place to another. A particular consequence of the law of conservation of energy is that the total energy of an isolated system does not change.

This states that energy can be neither created nor destroyed. However, energy can change forms, and energy can flow from one place to another. A particular consequence of the law of conservation of energy is that the total energy of an isolated system does not change.

* The concept of [[internal energy]] and its relationship to temperature.

* The concept of [[internal energy]] and its relationship to temperature.<br>

::If a system has a definite temperature, then its total energy has three distinguishable components. If the system is in motion as a whole, it has [[kinetic energy]]. If the system as a whole is in an externally imposed force field (e.g. gravity), it has [[potential energy]] relative to some reference point in space. Finally, it has internal energy, which is a fundamental quantity of thermodynamics. The establishment of the concept of internal energy distinguishes the first law of thermodynamics from the more general law of conservation of energy.

::If a system has a definite temperature, then its total energy has three distinguishable components. If the system is in motion as a whole, it has [[kinetic energy]]. If the system as a whole is in an externally imposed force field (e.g. gravity), it has [[potential energy]] relative to some reference point in space. Finally, it has internal energy, which is a fundamental quantity of thermodynamics. The establishment of the concept of internal energy distinguishes the first law of thermodynamics from the more general law of conservation of energy.

If a system has a definite temperature, then its total energy has three distinguishable components. If the system is in motion as a whole, it has kinetic energy. If the system as a whole is in an externally imposed force field (e.g. gravity), it has potential energy relative to some reference point in space. Finally, it has internal energy, which is a fundamental quantity of thermodynamics. The establishment of the concept of internal energy distinguishes the first law of thermodynamics from the more general law of conservation of energy.

If a system has a definite temperature, then its total energy has three distinguishable components. If the system is in motion as a whole, it has kinetic energy. If the system as a whole is in an externally imposed force field (e.g. gravity), it has potential energy relative to some reference point in space. Finally, it has internal energy, which is a fundamental quantity of thermodynamics. The establishment of the concept of internal energy distinguishes the first law of thermodynamics from the more general law of conservation of energy.

如果一个系统有一定的温度，那么它的总能量有三个可区分的组成部分。如果系统作为一个整体在运动，它就有动能。如果系统作为一个整体处于外部施加的力场中(例如:。重力) ，它相对于空间中某个参考点有势能。最后，它有内能，这是热力学的基本量。内能概念的建立使能量守恒定律不同于更一般的能量守恒定律。

 

  ——Solitude(讨论)

The internal energy of a substance can be explained as the sum of the diverse kinetic energies of the erratic microscopic motions of its constituent atoms, and of the potential energy of interactions between them. Those microscopic energy terms are collectively called the substance's internal energy, , and are accounted for by  macroscopic thermodynamic property. The total of the kinetic energies of microscopic motions of the constituent atoms increases as the system's temperature increases; this assumes no other interactions at the microscopic level of the system such as chemical reactions, potential energy of constituent atoms with respect to each other.

The internal energy of a substance can be explained as the sum of the diverse kinetic energies of the erratic microscopic motions of its constituent atoms, and of the potential energy of interactions between them. Those microscopic energy terms are collectively called the substance's internal energy, , and are accounted for by  macroscopic thermodynamic property. The total of the kinetic energies of microscopic motions of the constituent atoms increases as the system's temperature increases; this assumes no other interactions at the microscopic level of the system such as chemical reactions, potential energy of constituent atoms with respect to each other.

物质的内能可以解释为其组成原子不规则微观运动的不同动能和它们之间相互作用的势能的总和。这些微观能量项统称为物质的内能，并由宏观热力学性质列表解释。组成原子的微观运动动能的总和随着系统温度的升高而增加; 这在系统的微观层次上没有其他的相互作用，例如化学反应、组成原子相互间的势能。

物质的内能可以解释为其组成原子的不规则微观运动的不同动能和它们之间相互作用的势能的总和。这些微观能量统称为物质的内能，并由宏观热力学性质来解释。组成原子的微观运动的总和随着系统温度的升高而增加; 这假设在系统的微观层次上没有其他的相互作用，例如化学反应、组成原子相互间的势能。

* [[Work (physics)|Work]] is a process of transferring energy to or from a system in ways that can be described by macroscopic mechanical forces exerted by factors in the surroundings, outside the system. Examples are an externally driven shaft agitating a stirrer within the system, or an externally imposed electric field that polarizes the material of the system, or a piston that compresses the system. Unless otherwise stated, it is customary to treat work as occurring without its [[dissipation]] to the surroundings. Practically speaking, in all natural process, some of the work is dissipated by internal friction or viscosity. The work done by the system can come from its overall kinetic energy, from its overall potential energy, or from its internal energy.

* [[Work (physics)|Work]] is a process of transferring energy to or from a system in ways that can be described by macroscopic mechanical forces exerted by factors in the surroundings, outside the system. Examples are an externally driven shaft agitating a stirrer within the system, or an externally imposed electric field that polarizes the material of the system, or a piston that compresses the system. Unless otherwise stated, it is customary to treat work as occurring without its [[dissipation]] to the surroundings. Practically speaking, in all natural process, some of the work is dissipated by internal friction or viscosity. The work done by the system can come from its overall kinetic energy, from its overall potential energy, or from its internal energy.