Describe the manufacture of $H_2SO_4$ by the contact process.

(N/A) Sulphuric acid is manufactured by the contact process. It involves the following steps:
Step $(i):$
Sulphur or sulphide ores are burnt in air to form $SO_2$.
Step $(ii):$
By a reaction with oxygen,$SO_2$ is converted into $SO_3$ in the presence of $V_2O_5$ as a catalyst.
$2SO_{2(g)} + O_{2(g)} \xrightarrow{V_2O_5} 2SO_{3(g)}$
Step $(iii):$
$SO_3$ produced is absorbed in $H_2SO_4$ to give $H_2S_2O_7$ (oleum).
$SO_3 + H_2SO_4 \longrightarrow H_2S_2O_7$
This oleum is then diluted with water to obtain $H_2SO_4$ of the desired concentration.
In practice,the plant is operated at $2 \ bar$ pressure and $720 \ K$ temperature. The sulphuric acid thus obtained is $96-98 \%$ pure.