Explain the industrial manufacturing of sulphuric acid by the contact process.

(N/A) The contact process for the industrial manufacturing of sulphuric acid involves the following major steps:
$(i)$ Burning of sulphur or sulphide ores in the presence of air to generate $SO_{2}$ gas.
$(ii)$ Purification of $SO_{2}$ gas by removing dust and other impurities such as arsenic compounds.
$(iii)$ Catalytic oxidation of $SO_{2}$ with $O_{2}$ to form $SO_{3}$ in the presence of a vanadium pentoxide $(V_{2}O_{5})$ catalyst:
$2SO_{2(g)} + O_{2(g)} \rightleftharpoons 2SO_{3(g)}, \Delta_{r}H^{\ominus} = -196.6 \ kJ/mol$
This reaction is exothermic,reversible,and involves a decrease in volume. Therefore,low temperature and high pressure are favourable for maximum yield. In practice,the process is carried out at $2 \ bar$ pressure and $720 \ K$ temperature.
$(iv)$ Absorption of $SO_{3}$ in concentrated $H_{2}SO_{4}$ to produce oleum $(H_{2}S_{2}O_{7})$:
$SO_{3} + H_{2}SO_{4} \rightarrow H_{2}S_{2}O_{7}$
$(v)$ Dilution of oleum with water to obtain sulphuric acid of the desired concentration.
The sulphuric acid obtained by the contact process is $96-98 \%$ pure.