Cold packs are used by athletes to treat injuries. When a cold pack is activated, a chemical reaction occurs inside that causes the pack to feel cold. Explain why the pack feels cold, using ideas about bond breaking and bond forming.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Cold packs contain chemicals that react together when the pack is activated. Athletes press on the pack to start the reaction, and the surface of the pack rapidly drops in temperature.
Model answer (4 marks)
The reaction is endothermic. Breaking the bonds in the reactants requires more energy than is released when new bonds form in the products. The excess energy is absorbed from the surroundings – the pack and the athlete’s skin. Consequently the temperature of the pack and the surrounding area falls, so it feels cold.
Examiner tips
- Use the word ‘endothermic’ early to show you know the type of reaction.
- Explain the energy balance: more energy to break bonds than to form them.
- Show that the energy is taken from the surroundings, linking to the drop in temperature.
- Keep the answer concise – 4 marks can be earned with 3–4 short sentences.
Common mistakes
- Saying the reaction is exothermic – the opposite of what happens.
- Failing to mention that energy is taken from the surroundings, not released.
- Using vague terms like ‘heat is absorbed’ without linking to bond breaking/ forming.
Mark scheme (4 marks)
- The reaction taking place is endothermic
- More energy is needed/absorbed to break bonds in the reactants than is released when new bonds form in the products
- Energy is taken in from the surroundings (the pack / the athlete's skin)
- This causes the temperature of the surroundings / the pack to decrease, so it feels cold
Key terms in this question
Related
- All Edexcel GCSE Chemistry (1CH0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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