138. Differentiate between homogeneous catalysis and heterogeneous catalysis.

Homogeneous catalysis

Heterogeneous catalysis

1. When the reactants and the catalyst are in the same phase (i.e., liquid or gas), the process is said to be homogeneous catalysis.
for example:

Oxidation of sulphur dioxide into sulphur trioxide with dioxygen
in the presence of oxides of nitrogen as the catalyst in the lead
chamber process
$2{\mathrm{SO}}_2\left(\mathrm{g}\right) + {\mathrm{O}}_2\left(\mathrm{g}\right)\stackrel{\mathrm{NO}\left(\mathrm{g}\right)}{\to } 2{\mathrm{SO}}_3\left(\mathrm{g}\right)$

2. The reaction is assumed to proceed through the formation of an intermediate between the catalyst and one of the reactants.

 1. The catalytic process in which the reactant and the catalyst are in different phase is known as heterogenous.

Oxidation of sulphur dioxide into sulphur trioxide in the
presence of Pt.

$2{\mathrm{SO}}_2\left(\mathrm{g}\right) \stackrel{\mathrm{pt}\left(\mathrm{s}\right)}{\to } 2{\mathrm{SO}}_3\left(\mathrm{g}\right)$

2. The reaction proceeds through the adsorption of one or more reactants over the surface of the catalyst.