# Fermentation is a process used to produce ethanol from glucose. During fermentation, yeast breaks down glucose in the absence of oxygen. A student notices that the reaction vessel feels slightly warm to the touch during fermentation. The student also learns that when baking bread, the same fermentation process occurs inside the dough. Explain what the temperature change tells us about the energy change during fermentation, and describe what happens to bonds during the reaction that accounts for this overall energy change.

> OCR A-Level Chemistry A (H432) — 3.2 Physical chemistry · Explain · 5 marks

> Fermentation can be represented by the following equation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂. The reaction vessel feels warm to the touch during fermentation.

## Mark scheme (5 marks)

1. The reaction vessel feeling warm indicates energy is transferred to the surroundings
2. Fermentation is an exothermic reaction
3. Bond breaking occurs in the reactants (glucose) and requires energy / is endothermic
4. Bond making occurs when the products form and releases energy / is exothermic
5. The energy released in bond making is greater than the energy required for bond breaking, giving a net release of energy / overall energy change is negative

## Related

- [Revision notes for OCR A-Level Chemistry A (H432)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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