Abstract In this paper, firstly the reason for students making mistake on a problem frequently was analyzed. It has been found that two basic concepts (the standard states for species and the standard changes for reactions) need to be emphatically explained. And then according to some textbooks and references,when introducing chemical reaction isotherm equation, it may be better to introduce reaction quotient (Q) as activity quotient, and introduce the meaning of activity and activity calculation formulas of species in different reaction systems.