A student investigates the effect of surface area on the rate of reaction between zinc and sulfuric acid. In one experiment, a large single piece of zinc is used. In a second experiment, the same mass of zinc is used but cut into many small pieces. Explain why the reaction with small pieces of zinc is faster than the reaction with the large single piece.

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)

The small pieces of zinc give a larger total surface area than the single large piece.
This means more zinc atoms are exposed to the acid at any one time.
Consequently more acid‑zinc collisions occur per unit time.
The increased number of successful collisions raises the rate of reaction, so the reaction with the small pieces is faster.

Examiner tips

  • Show the chain of reasoning: surface area → more exposed atoms → more collisions → faster rate.
  • Use key terms: surface area, collisions, rate of reaction.
  • Keep the answer concise – 4 points can be covered in 4 short sentences.

Common mistakes

  • Using vague terms like "more zinc" instead of "greater surface area". Failing to link surface area to collision frequency. Writing a long paragraph instead of clear, separate points.

Mark scheme (4 marks)

  1. Small pieces of zinc have a greater (total) surface area than the large single piece
  2. More reactant particles (zinc/acid) are exposed / available for collisions at the surface
  3. There are more (successful) collisions between reacting particles per unit time / more frequent collisions
  4. Therefore the rate of reaction increases / reaction happens faster

Key terms in this question

surface area · rate of reaction

Related

More Rate and extent of chemical change questions

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