Explain in detail the manufacture of sulphuric acid by contact process.

It has 3 steps
1) Burning of sulphur in oxygen produces SO₂
$\mathrm{S}+{\mathrm{O}}_2\to {\mathrm{SO}}_2$
2) Sulphur dioxide is oxidized catalytically with atmospheric air to form SO₃
$2{\mathrm{SO}}_2+{\mathrm{O}}_2\stackrel{{\mathrm{V}}_2{\mathrm{O}}_5}{\to }2{\mathrm{SO}}_3$
3) Pure SO₃ is absorbed in 98% con H₂SO₄ to form oleum. Oleium is diluted with water to form sulphuric acid
$\begin{array}{l}{\mathrm{SO}}_3+{\mathrm{H}}_2{\mathrm{SO}}_4\to {\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_7\\ {\mathrm{H}}_2{\mathrm{S}}_2{\mathrm{O}}_7+{\mathrm{H}}_2\mathrm{O}\to 2{\mathrm{H}}_2{\mathrm{SO}}_4\end{array}$