The Contact process is used to manufacture sulfuric acid. One stage involves the equilibrium:

2SO₂(g) + O₂(g) ⇌ 2SO₃(g) ΔH = −196 kJ/mol

Industrial conditions typically use a temperature of 450°C and a pressure of 1–2 atm.

Why is a temperature of 450°C used rather than a lower temperature?

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Question

The Contact process is used to manufacture sulfuric acid. One stage involves the equilibrium:

2SO₂(g) + O₂(g) ⇌ 2SO₃(g)    ΔH = −196 kJ/mol

Industrial conditions typically use a temperature of 450°C and a pressure of 1–2 atm.

Why is a temperature of 450°C used rather than a lower temperature?

Accepted Answer

A lower temperature would give an unacceptably slow rate of reaction. — Award 1 mark for identifying that lower temperatures give slower rates despite better equilibrium yield. A is incorrect because lower temperature actually favours the exothermic forward reaction. B is incorrect because temperature does not directly poison catalysts. D is incorrect because lower temperatures would not decompose the product.

Answer

A lower temperature would shift equilibrium to the left.

Answer

A lower temperature would give an unacceptably slow rate of reaction.

Answer

A lower temperature would decompose the sulfur trioxide formed.

Answer

A lower temperature would cause the catalyst to become poisoned.

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