Also called effective concentration. In order to make the thermodynamics formula of ideal solution (or extremely dilute solution) applicable to real solution, it is used to replace a physical quantity of concentration. activity is the product of concentration and activity coefficient, is the effective concentration, and represents the activity degree of components in the system. The greater the activity, the higher the degree of chemistry, and the more prone to chemical changes.
Fundamental of Material Science -> Physical and chemical basis of materials