Question

Which one of the following statements is incorrect in the case of heterogeneous catalysts?
(A) The catalyst lowers the energy of activation
(B) The catalyst actually forms a compound with the reactant
(C) The surface of the catalyst plays a very important role.
(D) There is no change in the energy of activation

Answer 1

Catalysis are substances that help to increase the rate of reaction without consuming itself. They remain chemically and quantitatively unchanged after reaction.

Step by step answer: Catalysis one of two types:
(1) Homogeneous catalyst
(2) Heterogeneous catalyst
In Heterogeneous catalysis reactants and catalysts are in different phases.
Example:
Oxidation of $S{O_2}$to $S{O_3}$in presence of pt.
$2S{O_{2(g)}} + {O_{2(g)}}\xrightarrow{{p{t_{(g)}}}}2S{O_3}$
The reactant is in a gaseous state and the catalyst is in solid state.
Heterogeneous catalyst has following properties
(1) Diffusion of reactant to surface of catalyst
(2) Adsorphone reactant takes place on surface of catalyst
(3) For motion of intermediate takes place
(4) It lowers the activation energy of reaching species.
(5) Desorption of product takes place from catalyst surface
$\therefore$surface is again available for more reaction
$\therefore$The incorrect statement in case of heterogeneous catalysts is
There is no change in energy of activation

Therefore, from the above explanation the correct option is (D) There is no change in the energy of activation.

Additional Information: Homogenous catalysis is a process in which reactants and catalysts are in the same phase.
Example:
Hydrolysis of sugar is catalyzed by ${H^ + }$ ions given by sulphuric acid.
${C_{12}}{H_{22}}{O_{11}}(aq) + {H_2}O(l)\xrightarrow{{{H_2}S{O_4}(l)}}{C_6}{H_{12}}{O_6}(aq) + {C_6}{H_{12}}{O_6}(aq)$

Catalysts are highly selective in nature.
It means that a substance which acts as a catalyst in one reaction, may not act as a catalyst in another reaction.

Note: during the reaction the reactant gets adsorbed on the surface of the catalyst. This is a type of chemisorption in which reactants and catalysts are held together by chemical bonds.