Question

What is Heterogeneous catalysis? Give an example.

Answer 1

a substance which increases the rate of a reaction without itself undergoing ant permanent chemical change is known as catalyst and the phenomenon is known as catalysis. Catalysis is mainly two type. One is heterogeneous catalysis and other is homogeneous catalysis.

Complete step by step answer:
A catalyst actually participates in the chemical reaction and speeds up the reaction. Its temporary forms bond with the reactant and form an Activated complex.
Catalyst can be classified into two classes: (a) homogeneous catalysis and (b) heterogeneous catalysis.
1.Homogeneous catalysis: Catalysis in which the reactant and product are in the same phase is known as Homogeneous catalysis. E.g.- In the Lead chamber process for Sulphuric acid NO(g) is used as the catalyst. In this reaction Reactants are $S{O_2}$ (g) and ${O_2}$ (g). Both are in the gas phase. And the catalyst NO is also present in Gas phase.
In the hydrolysis of Sucrose (aq) into glucose (aq) and fructose (aq) using mineral acid. In this reaction. ${H_2}S{O_4}$ (aq) is used as the catalyst. Here, both the reactant and catalyst are in the liquid phase.
2.Heterogeneous catalysis: Catalysis in which the catalyst is in a phase different from that of the reactant is called Heterogeneous catalysis. E.g.- In the contact process of sulphuric acid Pt or ${V_2}{O_5}$ is used. When Pt or ${V_2}{O_5}$ is used to catalysis the combination of $S{O_2}$ (g) and ${O_2}$ (g) to form $S{O_3}$ (g), the reactants are in gas phase and the catalyst is present in solid phase.
In the Haber process for the manufacture of ammonia finely divided Fe is used as the catalyst. When
Fe (s) is used as the catalyst for the combination of and the reactants are in the gaseous phase and catalyst is present in the solid phase.

Note: Catalysts have General characteristics. Catalysts remain unchanged at the end of the reaction. Small amount of catalyst can increase the rate of reaction. A catalyst does not affect the position of equilibrium of a reversible reaction. This is because it speeds up the forward and backward reactions to the same extent. A catalyst speeds up only spontaneous reaction, not a non-spontaneous reaction.