Catalyst is a substance that changes the rate of a reaction and this
phenomenon is called catalysis. A catalyst affect the rate of the
reaction but itself remains unchanged in mass and properties at the end
of the reaction.
Catalysis is classified into following two categories
(i) Homogeneous catalysis:
The physical state (phase) of the catalyst is same as the physical state of reagents.
2SO2(g)+O2(g)NO(g)−−−−→2SO3(g)
CH3COOCH3(l)+H2O(l)HCl(l)−−−−→CH3COOH(l)+CH3OH(l)
(ii) Heterogeneous catalysis:
The
physical states (phases) of the catalyst reagents are different.
Generally, the catalyst is in solid phase (powdered form) and the
catalysis is called surface catalysis.
2SO2(g)+O2(g)Pt(s)−−−→2SO3(g)
N2(g)+3H2(g)Fe(s)−−−→2NH3(g)