What is the contact process?

An industrial method for manufacturing sulfuric acid involving three main steps: burning sulfur, oxidizing SO₂ to SO₃, and converting SO₃ to H₂SO₄.

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What is produced in the first step of the contact process?

Sulfur dioxide (SO₂) is produced by the combustion of sulfur with oxygen.

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What is the chemical equation for the combustion of sulfur?

S₈ + 8O₂ → 8SO₂

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How is sulfur dioxide converted to sulfur trioxide in the contact process?

By oxidising SO₂ using a vanadium(V) oxide catalyst:


2SO₂ + O₂ ⇄ 2SO₃.

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What role does a catalyst play in the oxidation of SO₂ to SO₃?

The catalyst speeds up the reaction rate without altering the equilibrium position.

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How is sulfuric acid (H₂SO₄) formed in the contact process?

By reacting sulfur trioxide (SO₃) with water:


SO₃ + H₂O → H₂SO₄.

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What temperature is optimal for the contact process?

Around 450°C to balance between reaction rate and yield.

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What pressure is typically used in the contact process?

A pressure around 2 atmospheres is used to balance yield and cost.

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Why are high temperatures not always used in the contact process?

High temperatures increase reaction rate but decrease yield due to shifting equilibrium.

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