A student adds a small piece of marble (calcium carbonate) to excess hydrochloric acid. The reaction produces carbon dioxide gas. Explain how increasing the surface area of the marble, by breaking it into smaller pieces, increases the rate of this reaction.

Eduqas GCSE Chemistry — C6 Rate and extent of chemical change · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

Breaking the marble into smaller pieces increases the surface area exposed to the acid.
More reactant particles are exposed/available at the surface for collisions.
This leads to a greater frequency of successful collisions.
Therefore the rate of reaction increases.

Examiner tips

  • Use the word "exposes" to show surface area increase. Show the chain: surface area → more collisions → higher rate. Keep the answer concise and use the exact terms from the mark scheme.

Common mistakes

  • Failing to mention surface area. Using vague terms like "more reactants" without linking to collisions. Writing in a narrative style instead of concise points.

Mark scheme (4 marks)

  1. Breaking the marble into smaller pieces increases the surface area exposed to the acid
  2. More reactant particles are exposed / available at the surface for collisions
  3. This leads to a greater frequency of successful collisions
  4. Therefore the rate of reaction increases

Key terms in this question

surface area

Related

More Rate and extent of chemical change questions

▶ Try answering this question with AI marking (free) →