A catalyst increases the rate of a reaction by providing an alternative route with a lower activation energy. In a reversible reaction it lowers the activation energy of the forward and reverse reactions by the same amount.As a result, the rates of the forward and reverse reactions increase by the same factor. The equilibrium concentrations are unchanged, so a catalyst does not affect the value of Kc and the position of equilibrium does not move.The only effect of a catalyst on an equilibrium is that equilibrium is reached more quickly. The same equilibrium mixture is obtained, but in less time.Kc is changed only by temperature. Changing concentration or pressure can shift the position of equilibrium, and a catalyst changes how fast equilibrium is reached, but none of these change Kc.This matters in industry. For an exothermic reaction such as the Haber process, a low temperature gives a large Kc but a slow rate. An iron catalyst gives a reasonable rate at a lower temperature than would otherwise be needed, so a better yield can be obtained economically.