# A student investigates the combustion of methane. The student knows that during the reaction, bonds in the reactants are broken and new bonds in the products are formed. Explain why the combustion of methane is an exothermic reaction, referring to bond breaking and bond making in your answer.

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

> The combustion of methane can be represented by the following equation: CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g)

## Mark scheme (5 marks)

1. Bond breaking is an endothermic process / energy is taken in to break bonds in the reactants
2. Bond making is an exothermic process / energy is released when bonds form in the products
3. More energy is released in bond making than is taken in during bond breaking
4. The overall energy change is negative / energy is transferred to the surroundings
5. In an exothermic reaction the energy of the products is lower than the energy of the reactants

## Key terms

- [exothermic reaction](https://www.gradenine.co.uk/glossary/exothermic-reaction)
- [bond breaking](https://www.gradenine.co.uk/glossary/bond-breaking)
- [bond making](https://www.gradenine.co.uk/glossary/bond-making)

## 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)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-investigates-the-combustion-of-79f6e7a3) · Published by Druglandscape Ltd.