Abstract: In teaching, it is found that the comprehensive calculation of the first law and the second law of thermodynamics causes difficulties for students. The problem can be solved from the two aspects of process type and process reversibility in this article. According to the difference of initial and final states, it is judged whether it is a simple change process, a phase change process or a chemical change process. Based on isothermal process, isobaric process, isochoric process, adiabatic process, etc., the calculation formulas of W, Q, △U, △H, △S, △A, △G are derived. For the same initial and final states, the W and Q of reversible and irreversible processes are different, while △U, △H, △S, △A, △G are the same. The problem-solving ideas and methods introduced in this article are expected to be helpful to students.

Key words: Laws of thermodynamics, Process classification, Reversible process, Comprehensive calculation