In a chemical reaction chemical equilibrium is defined as the state at which there is no further change in concentration of reactants and products.For example,At equilibrium the rate of forward reaction is equal to the rate of backward reaction. Equilibrium\xa0mixture:\xa0The mixture of reactants and products in the equilibrium state is called an equilibrium mixtures.Based on the extent to which the reactions proceed to reach the state of equilibrium, these may be classified in three groups:(i) The reactions which proceed almost to completion and the concentrations of the reactants left are negligible.(ii) The reactions in which most of the reactants remains unchanged, i.e. only small amounts of products are formed.(iii) The reactions in which the concentrations of both the reactants and products are comparable when the system is in equilibrium.