The contact process is used industrially to manufacture sulfuric acid. Explain why the conditions used in the contact process represent a compromise, rather than the most extreme conditions possible.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Sulfuric acid is one of the most widely produced industrial chemicals in the world. It is manufactured using the contact process, which uses vanadium(V) oxide as a catalyst, a temperature of 450°C, and a pressure of 2 atm.
Model answer (4 marks)
A higher temperature would increase the rate of reaction, but the reaction is reversible and a higher temperature shifts the equilibrium towards the reactants, reducing the yield of ΣO₃. 450°C is therefore chosen as a compromise between a sufficient rate of reaction and an acceptable yield of ΣO₃. The vanadium(V) oxide catalyst is used to increase the rate of reaction without affecting the yield or the position of equilibrium.
Examiner tips
- Use the word ‘compromise’ in your answer
- Explain the effect of temperature on rate and equilibrium
- Mention the catalyst’s role
- Keep the answer concise and to the point
Common mistakes
- Confusing the catalyst with the temperature effect on equilibrium
- Forgetting to mention that the catalyst does not change the equilibrium position
- Using vague phrases like ‘good conditions’ instead of specific temperature and pressure
Mark scheme (4 marks)
- A higher temperature would increase the rate of reaction / speed up the reaction
- But the reaction is reversible, so a higher temperature shifts the equilibrium towards the reactants / reduces the yield of sulfur trioxide
- 450°C is chosen as a compromise between a sufficient rate of reaction and an acceptable yield of sulfur trioxide / product
- The vanadium(V) oxide catalyst is used to increase the rate of reaction without affecting the yield / position of equilibrium
Key terms in this question
Related
- All OCR GCSE Chemistry A: Gateway Science (J248) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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