Question

Which is not the correct statement for a catalyst?
(A) It does not alter ${E_a}$.
(B) The surface of a catalyst adsorbs reactants.
(C) Catalyst may form intermediates with reactants.
(D) Action of enzyme catalysts is always specific.

Answer 1

As we know that a catalyst is basically a substance which can change the speed of a chemical reaction without itself undergoing any change in mass and chemical composition at the end of the reaction and the phenomenon is known as catalysis.

Complete answer: As we have already discussed that a catalyst is a substance which accelerates the rate of a chemical reaction and itself does not undergo any change in its chemical composition as well as its mass but it can change its physical state. It accelerates the rate of a reaction by basically lowering the activation energy.
The modern adsorption theory is the combination of intermediate compound formation theory and the old adsorption theory. The mechanism involves some steps. The first step is diffusion of reactants to the surface of the catalyst. The second one is adsorption of reactant molecules on the surface of the catalyst. Third, the occurrence of chemical reaction on the catalyst’s surface through formation of an intermediate. Now, a finely divided state of catalyst is more efficient for the reaction because the surface area increases and more adsorption takes place.
Also a catalyst is generally specific in nature and it cannot change the equilibrium state but it helps in attaining the equilibrium state more quickly.

Therefore the correct answer is (A).

Note: Remember that at a particular temperature the efficiency of a catalyst is maximum which is called optimum temperature. Also a catalyst does not change the enthalpy, Gibbs free energy and entropy of a reaction but it changes the activation energy by lowering its value significantly.