Hand warmers contain chemicals that undergo a reaction when activated. When a hand warmer is used, the temperature of the surroundings increases. State the type of reaction occurring in the hand warmer and explain, in terms of energy transfer, why the temperature of the surroundings increases.

Pearson Edexcel International GCSE Chemistry (4CH1) — 3.1 Energetics · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

The reaction is exothermic.
Energy is transferred from the reaction to the surroundings.
More energy is released when bonds are formed in the products than is required to break the bonds in the reactants.
This causes the temperature of the surroundings to rise.

Examiner tips

  • Use the word ‘exothermic’ first to show you know the reaction type. Show the energy flow: reaction → surroundings. Explain the bond energy difference. Link the energy release to the rise in temperature.

Common mistakes

  • Saying the reaction is endothermic. Failing to mention that energy moves to the surroundings. Confusing bond breaking with bond forming energy. Not connecting the energy release to the temperature rise.

Mark scheme (4 marks)

  1. The reaction is exothermic
  2. Energy is transferred from the reaction/chemicals to the surroundings
  3. Because more energy is released when bonds are formed in the products than is needed to break bonds in the reactants
  4. This causes the temperature of the surroundings to increase / rise

Key terms in this question

energy transfer · surroundings

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