Explain3 marksBGCSE
The same mass of marble reacts with the same volume and concentration of hydrochloric acid twice: once as large chips and once as a fine powder. Explain why the powder reacts faster.
Show the mark scheme and the examiner note
Answer: The powder has a much larger surface area, so acid particles collide with the marble more frequently per second, producing a faster rate.
- Powder has a greater surface area than chips for the same mass
- More frequent collisions between acid particles and the surface
- Rate is proportional to collision frequency, so the powder is faster
Examiner technique: Rate answers need the words "more frequent collisions". "More surface area" on its own explains the collision count and stops one mark short.