Whenever we hear the word Equilibrium immediately a picture arises in our mind an object under the influence of two opposing forces. For chemical reactions also this is true. A reaction also can exist in a state of equilibrium balancing forward and backward reactions.
In a chemical reaction, chemical equilibrium is the state in which the concentrations of the reactants and products have not yet changed with time. Usually, this state results when the forward reaction proceeds at the same rate as the reverse reaction. The reaction rates of the forward and reverse reactions are generally not zero but, being equal; there are no net changes in the concentrations of the reactant and product. This process is called dynamic equilibrium.