A sports injury pack is based on an endothermic reaction. When the pack is activated, its contents dissolve in water and the pack feels cold. Explain why the pack feels cold, using ideas about bonds and energy transfer to and from the surroundings.

Eduqas GCSE Chemistry — C5 Energy changes · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

1. Energy must be supplied to break the bonds in the reactants.
2. The energy required to break these bonds is greater than the energy released when new bonds are formed.
3. Therefore the reaction absorbs energy from the surroundings.
4. The surrounding temperature falls, so the pack feels cold.

Examiner tips

  • Use the word "absorb" to show energy uptake. Mention bond breaking before bond forming. Link the temperature drop to the pack feeling cold. Keep each point short and to the point.

Common mistakes

  • Confusing endothermic with exothermic. Saying the pack feels hot. Forgetting to mention bond breaking before bond forming.

Mark scheme (4 marks)

  1. Energy must be supplied to break bonds in the reactants
  2. The energy needed to break bonds is greater than the energy released when new bonds are formed
  3. The reaction takes in / absorbs energy from the surroundings
  4. The temperature of the surroundings decreases, which is why the pack feels cold

Key terms in this question

endothermic reaction · surroundings

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