# A student adds a small piece of marble (calcium carbonate) to dilute hydrochloric acid. The student then repeats the experiment using the same mass of marble, but crushed into a powder instead. Explain why the reaction with powdered marble is faster than the reaction with the small piece of marble.

> AQA A-Level Chemistry (7405) — 3.1.5 Kinetics · Explain · 5 marks

## Mark scheme (5 marks)

1. Powdering the marble increases the surface area (of the marble / reactant)
2. More (marble) particles are exposed to / in contact with the acid
3. There are more frequent collisions between (acid / hydrochloric acid) particles and (marble / calcium carbonate) particles
4. More collisions are successful / result in a reaction (per unit time)
5. Therefore the rate of reaction increases

## Related

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