Write all the chemical reactions involved in the manufacture of sulphuric acid by contact process. 

Explanation

Contact process involves three steps :
(i) Sulphur or sulphide ore is burnt in air to get `SO_(2)`.
`S+O_(2) to SO_(2)`
`4FeS_(2)+11O_(2) to 2Fe_(2)O_(3)+8SO_(2)`
(ii) Catalytic oxidation of `SO_(2)` with `O_(2)` in the presence of `V_(2)O_(5)` catalyst gives sulphur trioxide `(SO_(3))`.
`2SO+O_(2)overset(V_(2)O_(5))(to)2SO_(3)" "Delta_(f)H^(@)=-196.6" kJ/mol"`
According to Le Chatelier.s principle, this reaction is favoured at low temperature and high pressure.
(iii) `SO_(3)` obtained from catalytic converter is absorbed in conc. `H_(2)SO_(4)` to produce oleum. Oleum is diluted with water to get `H_(2)SO_(4)` of desired concentration.
`H_(2)SO_(4)+SO_(3)toH_(2)S_(2)O_(7)`
`H_(2)S_(2)O_(7)+H_(2)Oto2H_(2)SO_(4)`.