|Class 12 Chemistry Surface Chemistry||Catalysis|
Substances which alter the rate of a chemical reaction and themselves remain chemically and quantitatively unchanged after the reaction are called catalysts.
Example- In Haber’s process for manufacturing ammonia, molybdenum acts as promoter for the catalyst- iron
N2 (g) + 3H2 (g) --> 2NH3 (g)
Homogenous and Heterogeneous Catalysis
Catalysis can be classified into 2 types.
The reactants and the catalyst are in the same phase (that is liquid or gas).
Example- In Oxidation of sulphur dioxide,
Sulphur dioxide, oxygen and the catalyst nitrogen oxide are all gases
2SO2(g) + O2(g) à 2SO3 (g)
The reactants and the catalyst are in different phases
Example- In Oxidation of ammonia,
Ammonia and oxygen are gases but the catalyst Platinum is solid
4NH3(g) +5O2(g) --> 4NO(g) + 6H2O(g)
Adsorption theory of Heterogeneous catalysis: