A student reacts zinc powder with dilute sulfuric acid. A second student carries out the same reaction using large zinc granules instead of zinc powder, keeping all other conditions identical. Explain why the reaction using zinc powder produces a faster rate of reaction than the reaction using large zinc granules.

Pearson Edexcel International GCSE Chemistry (4CH1) — 3.2 Rates of reaction · Explain · 4 marks · View as Markdown

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

Zinc reacts with dilute sulfuric acid to produce zinc sulfate solution and hydrogen gas.

Model answer (4 marks)

Zinc powder has a larger surface area than large granules, so more zinc atoms are exposed to the acid.

This means more reacting particles are available at the surface.

Consequently, collisions between zinc atoms and acid molecules are more frequent.

With more frequent successful collisions, the reaction rate is higher for the powder than for the granules.

Examiner tips

  • Use the word "surface area" and link it to "more reacting particles". Explain that increased collisions give a higher rate. Keep the answer concise and use the exact terminology from the mark scheme.

Common mistakes

  • Saying the powder reacts faster because it is more reactive, not because of surface area. Forgetting to mention the increased number of collisions. Using vague terms like "more zinc" without explaining surface area.

Mark scheme (4 marks)

  1. Zinc powder has a greater/larger surface area than zinc granules
  2. More reacting particles are exposed at the surface
  3. This leads to more frequent collisions between zinc particles and acid particles
  4. There are more frequent successful collisions, so the rate of reaction increases

Key terms in this question

rate of reaction

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