CBSE Class 12-science Answered

If the catalyst is present in the different phase than that of the reactants, it is called a heterogeneous catalyst and

this type of catalysis is called heterogeneous catalysis.

• The catalyst in heterogeneous catalysis, catalyst is in solid and the reactants are gases or liquids.

• Also, the reaction takes place at the surface of the solid catalyst hence it is called as surface catalysis.

• According to old adsorption theory, it was assumed that the reactants in the gaseous state or from the solutions are adsorbed on the surface of the catalyst.

• Because of this, the concentration of the reactant molecules on the surface increases and the rate of reaction also increases.

• Adsorption is exothermic hence the heat evolved during the reaction is utilized to speed up the reaction.