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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.

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。

'''<font color="#ff8000"> 热力学第一定律first law of thermodynamics</font>''':当能量以'''<font color="#ff8000"> 功work</font>'''、'''<font color="#ff8000"> 热heat</font>'''或物质的形式进入或离开一个系统时，系统的'''<font color="#ff8000"> 内能 internal energy</font>'''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。

'''<font color="#ff8000"> 热力学第二定律second law of thermodynamics</font>''':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。

'''<font color="#ff8000"> 热力学第三定律third law of thermodynamics</font>''':当温度趋于'''<font color="#ff8000"> 绝对零度absolute zero</font>'''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。

{{quote|If two systems are both in thermal equilibrium with a third system then they are in thermal equilibrium with each other.<ref>Guggenheim (1985), p.&nbsp;8.</ref>}}

{{quote|If two systems are both in thermal equilibrium with a third system then they are in thermal equilibrium with each other.<ref>Guggenheim (1985), p.&nbsp;8.</ref>}}<br>

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.

 

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 .

在封闭系统的两级热力学循环中，该循环回到其原始状态，在循环的一个阶段向系统提供的热量{{math|''Q_in''}}，减去另一个阶段从系统中去除的热量{{math|''Q_out''}}，加上对系统做的的热力学功{{math|''W_in''}}，等于离开系统的做的热力学功{{math|''W_out''}}。

在封闭系统的两级'''<font color="#ff8000"> 热力循环thermodynamic cycle</font>'''中，该循环回到其原始状态，在循环的一个阶段向系统提供的热量{{math|''Q_in''}}，减去另一个阶段从系统中去除的热量{{math|''Q_out''}}，加上对系统做的的热力学功{{math|''W_in''}}，等于离开系统的做的热力学功{{math|''W_out''}}。

A more general form of the third law that applies to a system such as a glass that may have more than one minimum microscopically distinct energy state, or may have a microscopically distinct state that is "frozen in" though not a strictly minimum energy state and not strictly speaking a state of thermodynamic equilibrium, at absolute zero temperature:

A more general form of the third law that applies to a system such as a glass that may have more than one minimum microscopically distinct energy state, or may have a microscopically distinct state that is "frozen in" though not a strictly minimum energy state and not strictly speaking a state of thermodynamic equilibrium, at absolute zero temperature:

第三定律的一个更普遍的形式，适用于一个系统，如玻璃，'''<font color="#32CD32">可能有一个以上的微观上截然不同的能量状态，或可能有一个微观上截然不同的“冻结状态”，虽然不是一个严格意义上的的最低能量状态，也不是严格意义上的热力学平衡，</font>'''在绝对零度:

第三定律的一个更普遍的形式，适用于像玻璃这样的系统，'''<font color="#32CD32">可能有一个以上的微观上截然不同的能量状态，或可能有一个微观上截然不同的“冻结状态”，虽然不是一个严格意义上的的最低能量状态，也不是严格意义上的热力学平衡，</font>'''在绝对零度:

:''The entropy of a system approaches a constant value as the temperature approaches zero.''

:''The entropy of a system approaches a constant value as the temperature approaches zero.''

The constant value (not necessarily zero) is called the residual entropy of the system.

The constant value (not necessarily zero) is called the residual entropy of the system.

这个常数(不一定是零)称为系统的余熵。

这个常数(不一定是零)被称为系统的余熵。

历史

历史

{{see also|Philosophy of thermal and statistical physics}}

{{see also|Philosophy of thermal and statistical physics}}<br>

[[Mechanical equivalent of heat|Circa 1797, Count Rumford (born Benjamin Thompson)]] showed that endless mechanical action can generate indefinitely large amounts of heat from a fixed amount of working substance thus challenging the caloric theory of heat, which held that there would be a finite amount of caloric heat/energy in a fixed amount of working substance. The first established thermodynamic principle, which eventually became the second law of thermodynamics, was formulated by [[Nicolas Léonard Sadi Carnot|Sadi Carnot]] in 1824. By 1860, as formalized in the works of those such as [[Rudolf Clausius]] and [[William Thomson, 1st Baron Kelvin|William Thomson]], two established principles of thermodynamics had evolved, the first principle and the second principle, later restated as thermodynamic laws.  By 1873, for example, thermodynamicist [[Josiah Willard Gibbs]], in his memoir ''Graphical Methods in the Thermodynamics of Fluids'', clearly stated the first two absolute laws of thermodynamics.  Some textbooks throughout the 20th century have numbered the laws differently.  In some fields removed from chemistry, the second law was considered to deal with the efficiency of heat engines only, whereas what was called the third law dealt with entropy increases.  Directly defining zero points for entropy calculations was not considered to be a law.  Gradually, this separation was combined into the second law and the modern third law was widely adopted.

[[Mechanical equivalent of heat|Circa 1797, Count Rumford (born Benjamin Thompson)]] showed that endless mechanical action can generate indefinitely large amounts of heat from a fixed amount of working substance thus challenging the caloric theory of heat, which held that there would be a finite amount of caloric heat/energy in a fixed amount of working substance. The first established thermodynamic principle, which eventually became the second law of thermodynamics, was formulated by [[Nicolas Léonard Sadi Carnot|Sadi Carnot]] in 1824. By 1860, as formalized in the works of those such as [[Rudolf Clausius]] and [[William Thomson, 1st Baron Kelvin|William Thomson]], two established principles of thermodynamics had evolved, the first principle and the second principle, later restated as thermodynamic laws.  By 1873, for example, thermodynamicist [[Josiah Willard Gibbs]], in his memoir ''Graphical Methods in the Thermodynamics of Fluids'', clearly stated the first two absolute laws of thermodynamics.  Some textbooks throughout the 20th century have numbered the laws differently.  In some fields removed from chemistry, the second law was considered to deal with the efficiency of heat engines only, whereas what was called the third law dealt with entropy increases.  Directly defining zero points for entropy calculations was not considered to be a law.  Gradually, this separation was combined into the second law and the modern third law was widely adopted.