Introduction of equilibrium state
Equilibrium state refers to a state in which the macroscopic properties of various parts of a thermodynamic system do not change over a long period of time without external influence. The term “no external influence” mentioned here refers to the fact that the system has no interaction with the outside world. It has neither material exchange nor energy transfer (work and heat transfer), that is, the system is an isolated system.
The equilibrium state is a state in which the state variables of the system under investigation remain unchanged. The actual system is always subject to different degrees of perturbation (perturbation), and it can only be observed if it can return to an equilibrium state after a certain degree of perturbation. This state is a stable equilibrium state. The narrow equilibrium state refers to a stable equilibrium state.