Gold is unreactive in bulk, but gold nanoparticles can catalyse some reactions. A student measured the rate of a reaction using the same mass of gold in particles of different sizes. For the same mass of gold, total surface area is proportional to 1diameter\dfrac{1}{\text{diameter}}diameter1.
| Particle diameter (nm) | 40 | 20 | 10 | 5 |
|---|---|---|---|---|
| Relative rate | 1.0 | 2.0 | 4.0 | 15 |
Which conclusion is best supported by the data?
The rate is proportional to the total surface area of the gold for all four particle sizes
Smaller particles have a smaller surface area to volume ratio, so surface area cannot explain the trend
Surface area explains the trend down to 10 nm, but 5 nm particles are more active than it predicts
The 5 nm result must be an error, because surface area alone predicts a relative rate of 8.0
36 exam-style questions on Edexcel GCSE Chemistry 10.5 Bulk and surface properties of matter including nanoparticles, covering 10.5.1 Nanoparticles: size, uses and risks and 10.5.2 Comparing and selecting materials. Each one has a worked solution and a mark scheme showing where the marks go.