# A student is investigating the rate at which marble chips (calcium carbonate) react with hydrochloric acid. The student uses large marble chips in one experiment and then repeats the experiment using powdered marble of the same mass. Explain why the powdered marble reacts faster than the large marble chips.

> OCR GCSE Chemistry A: Gateway Science (J248) — C5.2 Controlling reactions · Explain · 4 marks

> Marble chips and powdered marble are both calcium carbonate. When the same mass of each is reacted with excess hydrochloric acid, the powdered marble produces gas at a faster rate than the large marble chips.

## Mark scheme (4 marks)

1. Powdered marble has a greater surface area (to volume ratio) than large marble chips
2. More reacting particles are exposed (at the surface)
3. There are more frequent collisions between reactant particles
4. This leads to a higher rate of successful collisions and therefore a faster rate of reaction

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