# The Contact process is used to manufacture sulfuric acid. One stage involves the reaction of sulfur dioxide with oxygen to form sulfur trioxide. This reaction reaches a dynamic equilibrium. Explain what is meant by the term 'dynamic equilibrium' and describe how the equilibrium position can be altered to increase the yield of sulfur trioxide.

> Edexcel GCSE Chemistry (1CH0) — 9.3 Dynamic equilibria, calculations involving volumes of gases (Chem only) · Explain · 4 marks

> In the Contact process, sulfur dioxide and oxygen react reversibly to form sulfur trioxide: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g). The forward reaction is exothermic.

## Mark scheme (4 marks)

1. The forward and reverse reactions are both occurring / the reaction proceeds in both directions simultaneously
2. The rate of the forward reaction equals the rate of the reverse reaction
3. Decreasing the temperature shifts the equilibrium position to the right / towards the exothermic (forward) reaction, increasing the yield of sulfur trioxide
4. Increasing the pressure shifts the equilibrium position to the right / towards fewer moles of gas, increasing the yield of sulfur trioxide

## Key terms

- [dynamic equilibrium](https://www.gradenine.co.uk/glossary/dynamic-equilibrium)
- [equilibrium position](https://www.gradenine.co.uk/glossary/equilibrium-position)
- [yield](https://www.gradenine.co.uk/glossary/yield)

## Related

- [Revision notes for Edexcel GCSE Chemistry (1CH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/the-contact-process-is-used-to-5ff62b71) · Published by Druglandscape Ltd.