(i) The catalyst remains unchanged in amount and chemical composition at the end of the reaction; it may, however, undergo considerable change in physical form.
(ii) A small quantity of the catalyst is capable of producing the desired effect.
(iii) The action of a catalyst is specific to a large extent. Thus, the decomposition of KCIO3 is catalyzed by MnO2 but not by platinum.
(iv) The catalyst does not initiate a reaction; it merely accelerates the reaction that is already occurring.
(v) A catalyst does not alter the final state of equilibrium in a reversible reaction.
A certain minimum energy must be possessed by the reactants so that they may react and produce the products. This is called the activation energy (Ea) for the reaction. A catalyst is said to lower the activation energy and thus increase the rate of the reaction.
Thus, a catalyst increases the rate of a reaction by providing a pathway whose activation energy is lower than the activation energy of the uncatalysed reaction.