Abstract: The entropy change of a system can be used to determine the direction of a process, which plays an important role in teaching thermodynamics. There are diversity and flexibility in the problems about calculation of entropy change, which are the difficulties in teaching. Four kinds of problems of calculation of entropy changes have been discussed by the case study of problems including entropy changes of reversible and irreversible process, entropy changes of mixing process of ideal gases, entropy changes of system and surroundings, and entropy changes of cyclic processes. How to solve the problems of entropy changes has been illustrated by using the related knowledge about the first and second law of thermodynamics, especially the three aspects of knowledge concerning entropy.

Key words: calculation of entropy changes, reversible process, state function