Explain why breaking a large lump of a solid reactant into smaller pieces increases the rate of a chemical reaction.

Cambridge International IGCSE Chemistry (0620) — 6.2 Rate of reaction · Explain · 4 marks · View as Markdown

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

When a solid reactant is used in a chemical reaction, the size of the pieces can affect how quickly the reaction proceeds.

Model answer (4 marks)

Breaking a solid into smaller pieces increases its surface area, so more of the solid is exposed to the other reactant. This means more solid particles are available to collide with the other reactant’s particles. Consequently, the frequency of successful collisions rises, which increases the rate of reaction.

Examiner tips

  • Use the word ‘surface area’ and link it to more exposed particles. Mention that more collisions occur. Show the chain: surface area → more exposed particles → more collisions → higher rate.
  • common_mistakes
  • :
  • Failing to mention surface area. Saying only ‘more particles’ without explaining collision frequency. Using vague phrases like ‘makes it faster’ without the mechanistic link.

Mark scheme (4 marks)

  1. Breaking into smaller pieces increases the surface area (of the solid / exposed to the other reactant)
  2. More particles of the solid are exposed / available to collide with particles of the other reactant
  3. There is a greater frequency of (successful) collisions between reactant particles
  4. Therefore the rate of reaction increases

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