# Hydrogen peroxide solution decomposes slowly at room temperature into water and oxygen. When a small amount of manganese dioxide is added, the reaction speeds up and the surroundings feel warm. Explain what type of energy change is occurring and why the temperature of the surroundings increases. In your answer, state what happens to the bonds in the reactants and the bonds formed in the products.

> AQA A-Level Chemistry (7405) — 3.1.4 Energetics · Explain · 5 marks

> Hydrogen peroxide solution decomposes slowly at room temperature into water and oxygen. When a small amount of manganese dioxide is added, the reaction speeds up and the surroundings feel warm.

## Mark scheme (5 marks)

1. The reaction is exothermic
2. Energy is required / taken in to break bonds in the reactants (hydrogen peroxide)
3. Energy is released when bonds are formed in the products (water and oxygen)
4. More energy is released forming bonds in the products than is required to break bonds in the reactants
5. The surplus energy is transferred to the surroundings, so the temperature of the surroundings increases

## Key terms

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

## Related

- [Revision notes for AQA A-Level Chemistry (7405)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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