Hand warmers contain iron powder. When a hand warmer is activated, iron reacts with oxygen in the air. The hand warmer becomes hot to the touch. Explain why the hand warmer becomes hot, and describe what this tells us about whether bonds are broken or formed during the reaction.

OCR GCSE Chemistry A: Gateway Science (J248) — C3.3 Types of chemical reactions · Explain · 4 marks · View as Markdown

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

Hand warmers are single-use packets used by hikers and skiers to keep their hands warm in cold conditions. Inside each packet is iron powder that reacts when exposed to air.

Model answer (4 marks)

The reaction is exothermic, so energy is released.
The released energy is transferred to the surroundings, raising the temperature of the hand warmer.
In an exothermic reaction, the energy released when new bonds are formed exceeds the energy required to break the original bonds.
Thus, bond making releases energy, making the process exothermic.

Examiner tips

  • Use the word ‘exothermic’ and link it to heat release. Show the energy flow: breaking bonds (endothermic) < forming bonds (exothermic). Mention that the temperature rise is evidence of energy transfer to surroundings.
  • common_mistakes
  • :
  • Saying the reaction is endothermic or that energy is absorbed. Failing to explain that bond formation releases energy. Omitting the link between energy release and temperature increase.

Mark scheme (4 marks)

  1. The reaction is exothermic
  2. Energy is transferred to the surroundings, causing the temperature to increase
  3. In an exothermic reaction, more energy is released making bonds than is taken in breaking bonds
  4. Bond making releases energy / bond making is an exothermic process

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