Changing the surface area of the reactants
3 marks · NormalA factory grinds solid reactants used in a chemical process into fine powder instead of using large lumps. Explain, with reasons, how and why this affects the rate of the reaction.
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Must show: Relates fine powder to surface area, Links surface area to collision frequency, States faster rate as a result
Also accept: Explanation using examples like 'more reactant exposed,' as long as cause and effect are explained.
Common mistakes: Only stating 'smaller pieces react faster' without reasoning.
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Marking points
R1 · 1 mark · States that a fine powder increases the surface area.
R2 · 1 mark · Explains that more particles are exposed to react (or more collisions possible).
R3 · 1 mark · Links this to a faster rate of reaction (collisions per unit time greater).
Worked solution
Grinding reactants into a fine powder increases their surface area.
More of the reactant particles are exposed and available for reaction with other chemicals.
This means there are more collisions per second between reactant particles, so the rate of the reaction increases.