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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''' <font color = 'red'><s>对</s></font> <font color = 'blue'>定义了</font>热力学系统所涉及到的'''内能 Internal Energy'''<font color = 'red'><s>进行了定义</s></font> ，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<font color = 'red'><s>设定</s></font> <font color = 'blue'>断言</font>自然过程只在一种意义上进行，且<font color = 'red'><s>是</s></font> 不可逆<font color = 'red'><s>的</s></font> 。例如，当有了传导和辐射的（传播）路径时，热<s>量</s>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 = 'red'>若一个孤立系统最初在内部不可渗透的薄膜维持内部的热力学平衡，通过一些操作使得薄膜具有渗透性，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，其总熵增加。</font>

'''热力学第一定律 First Law Of Thermodynamics''' <font color = 'red'><s>对</s></font> <font color = 'blue'>定义了</font>热力学系统所涉及到的'''内能 Internal Energy'''<font color = 'red'><s>进行了定义</s></font> ，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<font color = 'red'><s>设定</s></font> <font color = 'blue'>断言</font>自然过程只在一种意义上进行，且<font color = 'red'><s>是</s></font> 不可逆<font color = 'red'><s>的</s></font> 。例如，当有了传导和辐射的（传播）路径时，热<s>量</s>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 = 'red'><s>若一个孤立系统最初在内部不可渗透的薄膜维持内部的热力学平衡，通过一些操作使得薄膜具有渗透性，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，其总熵增加。</s></font>

<font color = 'blue'>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。</font>

<font color = 'blue'>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。</font>