Question

How does a heterogeneous catalyst catalyse a chemical reaction? Explain in the light of adsorption theory.

Answer 1

A heterogeneous catalyst catalyses a chemical reaction by providing an active surface where reactant molecules (in a different phase) can adsorb. According to the adsorption theory, reactant molecules adhere to the catalyst’s surface, where their bonds are weakened, lowering activation energy. The reaction occurs more easily, and products are then desorbed, leaving the catalyst unchanged.

Example: In the Haber process, iron (solid) acts as a catalyst, and the gases nitrogen (N₂) and hydrogen (H₂) adsorb on its surface to form ammonia (NH₃).

\[\ce{N2_{(g)} + 3H2_{(g)} ->[Fe (solid)] 2NH3_{(g)}}\]