# Baking powder contains sodium hydrogencarbonate. When baking powder is added to cake mixture and placed in a hot oven, the sodium hydrogencarbonate decomposes to release carbon dioxide gas, causing the cake to rise. A student investigates this reaction by heating sodium hydrogencarbonate in a test tube and recording the temperature of the surroundings. She notices the temperature of the surroundings decreases during the reaction. Explain why the temperature of the surroundings decreases, and describe what this tells us about the bond breaking and bond making processes occurring during this reaction.

> OCR A-Level Chemistry B: Salters (H433) — 3.2 Physical chemistry · Explain · 5 marks

> Sodium hydrogencarbonate decomposes on heating to produce sodium carbonate, water and carbon dioxide.

## Mark scheme (5 marks)

1. The reaction is endothermic
2. Energy is taken in from the surroundings (causing the temperature of the surroundings to decrease)
3. More energy is required to break bonds in the reactants than is released when bonds are made in the products
4. Bond breaking is an endothermic process (requires energy input)
5. Bond making is an exothermic process (releases energy)

## Key terms

- [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 B: Salters (H433)](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/baking-powder-contains-sodium-hydrogencarbonate-when-78d96f73) · Published by Druglandscape Ltd.