Spontaneous process is an important concept of thermodynamics.It is combined with the second law of thermodynamics to indicate the direction of the process.So far,however,there is no satisfactory definition for spontaneous process.This has caused difficulties in the teaching of Physical Chemistry.In order to solve this problem,the examples of accepted spontaneous processes are analyzed and summarized.The problems existing in the current definition of spontaneous process are pointed out.It is pointed out that these problems are caused by the fact that people do not pay attention to the division of the system in the discussion of the spontaneous process.A clear definition of spontaneous process is obtained.The concept of non spontaneous processes that can occur under given conditions is derived.The convenient and practical direction criteria are given by combining these concepts with the second law of thermodynamics.The fuzziness of the previous spontaneous process definition is overcome.%自发过程是热力学的一个重要概念,它与热力学第二定律相结合可指明过程的方向,然而到目前为止自发过程还没有一个令人满意的定义,给物理化学教学带来了困难.为了解决此问题,针对公认的自发过程的例子进行了严格分析和总结,在此基础上指出了目前典型的自发过程定义存在的问题,指明这些问题是由人们在讨论自发过程例子时没有注意系统的划分而导致的.给出了意义明确的自发过程定义,引出了给定条件下能发生的非自发过程的概念.将这些概念和热力学第二定律相结合,得到方便实用的过程方向判据,克服了以往自发过程定义的模糊性.
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