Describe what happens to the temperature of the surroundings during an exothermic reaction and explain, in terms of energy transfer, why this change occurs. Give one example of an exothermic reaction.

Cambridge International IGCSE Chemistry (0620) — 5.1 Exothermic and endothermic reactions · Describe · 4 marks · View as Markdown

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

Model answer (4 marks)

The temperature of the surroundings rises.

Energy is released from the reacting substances and transferred to the surroundings.

The products possess lower internal energy than the reactants.

Example: combustion of methane, CH₄ + 2O₂ → CO₂ + 2H₂O + heat.

Examiner tips

  • Use the word ‘rise’ or ‘increase’ for the temperature change. Show the energy flow direction (from reaction to surroundings). Mention that product energy is lower. Give a clear, textbook example such as combustion of methane or burning of wood.

Common mistakes

  • Saying the temperature of the reaction mixture changes instead of the surroundings. Failing to state that energy is released to the surroundings. Giving an endothermic example such as photosynthesis.

Mark scheme (4 marks)

  1. The temperature of the surroundings increases during an exothermic reaction
  2. Energy is released / transferred from the reaction / chemicals to the surroundings
  3. The products have less / lower energy than the reactants
  4. Correct example of an exothermic reaction

Key terms in this question

exothermic · surroundings · energy transfer

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