When a self-heating can of coffee is activated, a chemical reaction occurs inside the can. Explain why the coffee heats up.

AQA GCSE Chemistry (8462) — 4.5.1 Exothermic and endothermic reactions · 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, so the energy released when new bonds are formed in the products is greater than the energy required to break the bonds in the reactants. The excess energy is transferred to the surroundings, raising their temperature. Consequently the coffee inside the can becomes hotter.

Examiner tips

  • Use the word ‘exothermic’ early to show understanding of the reaction type.
  • Explain the energy balance (bond breaking vs forming) to justify heat release.
  • Mention that the heat is transferred to the coffee, increasing its temperature.
  • Keep the answer concise and use correct terminology (e.g., ‘surroundings’, ‘energy released’).

Common mistakes

  • Confusing exothermic with endothermic, or stating the reaction is endothermic.
  • Failing to mention the energy balance between bond breaking and forming.
  • Using vague phrases like ‘the reaction heats up’ without explaining why.

Mark scheme (4 marks)

  1. The reaction is exothermic
  2. Energy is transferred to the surroundings
  3. The energy released when new bonds are formed (in the products) is greater than the energy needed to break bonds (in the reactants)
  4. So the temperature of the surroundings increases / the coffee gets hotter

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