How is H2SO4 manufactured by contact …

Step 1: Preparation of sulphur dioxide:

SO₂ is prepared by burning sulphur in the presence of excess air so that the product combines with oxygen which is helpful for the next stage.

S(s) + O₂ (g) → SO₂(g)

Step 2: Preparation of sulphur trioxide:

Sulphur trioxide is formed when sulphur dioxide reacts with oxygen in a ratio of 1:1 at a temperature of 400°C – 450°C and a pressure of 1-2 atm in the presence of N₂O₅ as a catalyst. This reaction is reversible in nature.

2SO₂(g) + O₂(g) ⇌ 2SO₃(g)

Step 3: Preparation of concentrated sulphuric acid:

The sulphur trioxide formed is first made to react with concentrated sulphuric acid. Sulphur trioxide cannot be dissolved in water directly as it leads to the formation of fog. The product obtained after this reaction is known as oleum. The oleum obtained is then dissolved in water to obtain concentrated sulphuric acid.

H₂SO₄ + SO₃(g) → H₂S₂O₇(l)

H₂S₂O₇(l) + H₂O(l) → 2H₂SO₄