A student investigated the reaction between a compressed block containing sodium hydrogencarbonate and citric acid solution. Carbon dioxide gas was produced.
The block was a cuboid measuring 12 mm×8 mm×4 mm12\ \text{mm} \times 8\ \text{mm} \times 4\ \text{mm}12 mm×8 mm×4 mm. Its surface area was 352 mm2.
In one experiment, the block was added whole. In a second experiment, an identical block was cut into cubes with sides of 2 mm. No material was lost when the block was cut.
The same volume and concentration of excess citric acid solution were used at the same temperature in both experiments.
| Form of the block | Volume of carbon dioxide produced in the first 20 s in cm3\text{cm}^3cm3 |
|---|---|
| Whole block | 30 |
| 2 mm cubes | 70 |
Calculate the percentage increase in the total surface area when the whole block was cut into cubes with sides of 2 mm.
Calculate how many times greater the mean rate of production of carbon dioxide was for the cubes than for the whole block during the first 20 s.
Explain the difference between the mean rates in part (b) and how cutting each 2 mm cube into eight cubes with sides of 1 mm would affect the rate.
127 exam-style questions on AQA GCSE Chemistry 6.1 Rate of reaction, covering 6.1.1a Calculating rates of reactions, 6.1.1b Gradient of a tangent as rate, 6.1.2 Factors which affect the rates of chemical reactions, 6.1.3 Collision theory and activation energy, and 6.1.4 Catalysts. Each one has a worked solution and a mark scheme showing where the marks go.