Describe the theory of manufacture of sulphuric acid by contact process, with all the necessary conditions (No technical details are required but equations should be given for each stage of process).
The theory of manufacture of sulphuric acid by contact process involves following steps:
i. Production of SO2 : SO2 is produced by burning sulphur or roasting iron pyrites.
S + O2 → SO2 Or
4FeS2 + 11O2 → 2Fe2O3 + 8SO2
ii. Catalytic oxidation of SO2 by air to give sulphur trioxide:
2SO2 + O2 ⇌ 2SO3 + Heat
iii. Absorption of sulphur trioxide in 98% sulphuric acid to form oleum:
SO3 + H2SO4 → H2S2O7
iv. Dilution of oleum to get sulphuric acid of desired concentration:
H2S2O7 + H2O → 2H2SO4