Asystem is said to be in when no net change in the amounts of reactants and products occurs.

A system is said to be in Equilbrium when no net change in the amounts of reactants and products occurs. This is referred to as the chemical equilbrium; a state of balance in which the rates of the forward and reverses reactions are equal; no net change in the amounts of reactants and products occurs in the chemical system. However when a stress is applied to a system at equilibrium, the system changes in a way that relieves the stress according to the Le Chatelier's principle.