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The first law of thermodynamics provides the definition of the internal energy of a thermodynamic system, and expresses the law of conservation of energy. The second law is concerned with the direction of natural processes. It asserts that a natural process runs only in one sense, and is not reversible. For example, when a path for conduction and radiation is made available, heat always flows spontaneously from a hotter to a colder body. Such phenomena are accounted for in terms of entropy. If an isolated system is held initially in internal thermodynamic equilibrium by internal partitioning impermeable walls, and then some operation makes the walls more permeable, then the system spontaneously evolves to reach a final new internal thermodynamic equilibrium, and its total entropy, S, increases.

The first law of thermodynamics provides the definition of the internal energy of a thermodynamic system, and expresses the law of conservation of energy. The second law is concerned with the direction of natural processes. It asserts that a natural process runs only in one sense, and is not reversible. For example, when a path for conduction and radiation is made available, heat always flows spontaneously from a hotter to a colder body. Such phenomena are accounted for in terms of entropy. If an isolated system is held initially in internal thermodynamic equilibrium by internal partitioning impermeable walls, and then some operation makes the walls more permeable, then the system spontaneously evolves to reach a final new internal thermodynamic equilibrium, and its total entropy, S, increases.

'''热力学第一定律 First Law Of Thermodynamics'''定义了热力学系统所涉及到的'''内能 Internal Energy''，并体现了能量守恒定律。热力学第二定律与'''自然过程Natural Processes'''的方向有关。它断言自然过程只在一种意义上进行，且不可逆 。例如，当有了传导和辐射的（传播）路径时，热总是自发地从一个较热的物体流向一个较冷的物体。这种现象可以用'''熵Entropy'''来解释。

'''热力学第一定律 First Law Of Thermodynamics'''定义了热力学系统所涉及到的'''内能 Internal Energy'''，并体现了能量守恒定律。热力学第二定律与'''自然过程Natural Processes'''的方向有关。它断言自然过程只在一种意义上进行，且不可逆 。例如，当有了传导和辐射的（传播）路径时，热总是自发地从一个较热的物体流向一个较冷的物体。这种现象可以用'''熵Entropy'''来解释。

'''<font color="#32CD32">若一个'''孤立系统Isolated System'''最初在具有隔热内壁的系统内维持热力学平衡，通过一些操作使内壁透热，则该系统可自发地演变，最终达到一个新的内部热力学平衡，且其总熵{{math|''S''}}增加。If an isolated system is held initially in internal thermodynamic equilibrium by internal partitioning impermeable walls, and then some operation makes the walls more permeable, then the system spontaneously evolves to reach a final new internal thermodynamic equilibrium, and its total entropy, S, increases.</font>'''

'''<font color="#32CD32">若一个'''孤立系统Isolated System'''最初在具有隔热内壁的系统内维持热力学平衡，通过一些操作使内壁透热，则该系统可自发地演变，最终达到一个新的内部热力学平衡，且其总熵{{math|''S''}}增加。If an isolated system is held initially in internal thermodynamic equilibrium by internal partitioning impermeable walls, and then some operation makes the walls more permeable, then the system spontaneously evolves to reach a final new internal thermodynamic equilibrium, and its total entropy, S, increases.</font>'''