Question

What is catalysis ? How is catalysis classified ? Give two examples for each type of catalysis.

Answer 1

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.
$2S{O}_2\left(g\right)+O_2\left(g\right)\stackrel{NO\left(g\right)}{\to }2S{O}_3\left(g\right)$
$C{H}_{3}COOC{H}_3\left(l\right)+H_{2}O\left(l\right)\stackrel{HCl\left(l\right)}{\to }C{H}_{3}COOH\left(l\right)+C{H}_{3}OH\left(l\right)$
(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.
$2S{O}_2\left(g\right)+O_2\left(g\right)\stackrel{Pt\left(s\right)}{\to }2S{O}_3\left(g\right)$
$N_2\left(g\right)+3H_2\left(g\right)\stackrel{Fe\left(s\right)}{\to }2N{H}_3\left(g\right)$