May/June 2026 Paper 21

2026 · 5 questions · 38 parts · 60 marks

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Context for question 2

The Contact process uses sulfur to produce sulfuric acid.

stage 1: Sulfur is burned in excess air.

stage 2 2 S O_{2} (g) + O_{2} (g) ⇌ 2 S O_{3} (g) Δ H = - 196 kJ mol^{- 1}

stage 3: SO

_{3}

reacts to produce H

_{2}

_{4}

2(a)Nitrogen Sulfur Industrial ProcessesEasy1 mark

Write an overall equation for stage 3.

Answer

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2(b)(i)Dynamic Equilibria Equilibrium ConstantsEasy1 mark

The reaction conditions for stage 2 include using a ratio of 1 mol SO

_{2}

to 1 mol O

_{2}

, and heat in the presence of V

_{2}

_{5}

. Stage 2 is repeated using a ratio of more than 1 mol SO

_{2}

to 1 mol O

_{2}

. Predict the effect on the percentage yield of SO

_{3}

at equilibrium. Use Le Chatelier's Principle to explain your answer.

Answer

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2(b)(ii)CatalysisMedium2 marks

Explain how V

_{2}

_{5}

affects the rate of reaction.

Answer

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2(c)(i)Atmospheric Chemistry Air PollutionEasy1 mark

CaCO

_{3}

and O

_{2}

are added to the waste gases from the Contact process before they escape. This prevents the release of SO

_{2}

into the atmosphere.

equation 1 2 C a C O_{3} + 2 S O_{2} + O_{2} \to 2 C a S O_{4} + 2 C O_{2}

State one environmental consequence of the release of SO

_{2}

(g) into the atmosphere.

Answer

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2(c)(ii)Gas LawsHard4 marks

Use the ideal gas equation to calculate the volume of O

_{2}

(g) that reacts with 0.500 mol of SO

_{2}

at 400

^{\circ}

C and 101 kPa in equation 1. Include units in your answer.

Answer

0 words