Explain how increasing the surface area of a solid reactant increases the rate of reaction.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Marble chips (calcium carbonate) react with hydrochloric acid. A student crushes the marble chips into a fine powder before adding them to the acid.
Model answer (4 marks)
Increasing the surface area of the marble chips exposes more of the solid to the acid, so more particles are available to collide with the acid molecules. This increases the frequency of collisions between the reacting particles. With more collisions, there are more successful collisions that lead to reaction. Consequently, the rate of reaction increases.
Examiner tips
- Use the term "surface area" and link it to "more particles exposed". Mention "frequency of collisions" and "successful collisions". Show the logical progression to the rate increase. Use correct chemical terminology (e.g., "reactant" and "collision" ).
Common mistakes
- Failing to mention the increase in collision frequency. Using vague phrases like "more reaction" without explaining the mechanism. Confusing surface area with mass or volume.
Mark scheme (4 marks)
- Increasing surface area means more (reacting) particles are exposed / available to collide
- There is a greater frequency of collisions (between reacting particles)
- There are more frequent successful collisions
- Therefore the rate of reaction increases
Key terms in this question
surface area · rate of reaction
Related
- All AQA GCSE Chemistry (8462) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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