# The manufacture of ethanol by the fermentation of glucose is a reversible reaction. Industrial chemists also produce ethanol by the direct hydration of ethene using steam, shown by the equation: C₂H₄(g) + H₂O(g) ⇌ C₂H₅OH(g). This reaction is exothermic in the forward direction. Explain how changing the temperature and pressure would each affect the position of equilibrium in this reaction, and state the direction in which the equilibrium would shift in each case.

> OCR A-Level Chemistry A (H432) — 5.1 Rates, equilibrium and pH · Explain · 5 marks

> In industry, ethanol can be produced by reacting ethene gas with steam at high temperatures and pressures in the presence of a catalyst. The forward reaction is exothermic. The equation for the reaction is: C₂H₄(g) + H₂O(g) ⇌ C₂H₅OH(g). Chemists must carefully control the conditions to maximise the yield of ethanol.

## Mark scheme (5 marks)

1. Increasing temperature shifts the equilibrium position in the direction of the endothermic reaction (the reverse/backward reaction)
2. This is because Le Chatelier's principle states the equilibrium moves to counteract the change (i.e. to absorb the extra heat energy by favouring the endothermic direction)
3. Decreasing temperature shifts the equilibrium in the direction of the exothermic reaction (the forward reaction), increasing the yield of ethanol
4. Increasing pressure shifts the equilibrium towards the side with the smaller number of moles of gas
5. Therefore, increasing pressure shifts equilibrium to the right (forward direction), increasing the yield of ethanol, because there is 1 mole of gas on the product side compared to 2 moles on the reactant side

## Key terms

- [reversible reaction](https://www.gradenine.co.uk/glossary/reversible-reaction)

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