Experiments to measure the rate of reaction
5 marks · HardA student performs an experiment to investigate the effect of temperature on the rate of reaction between marble chips and dilute hydrochloric acid. The reaction produces carbon dioxide gas, which is measured using a gas syringe. The student uses identical masses of marble chips and the same volume and concentration of acid at two different temperatures. The following data is recorded:
| Time / min | Volume of CO₂ at 20°C / cm³ | Volume of CO₂ at 40°C / cm³ |
|---|---|---|
| 0 | 0 | 0 |
| 1 | 18 | 40 |
| 2 | 27 | 60 |
| 3 | 31 | 62 |
| 4 | 33 | 62 |
Calculate the average rate of reaction at 20°C in the first 2 minutes. Show your working.
Compare the rates of reaction at the two temperatures using the data. Give one reason, based on particle collisions, why the temperature affects the rate of reaction.
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(a(i)) 13.5 cm³/min
(a(ii)) The reaction at 40°C is faster, producing more CO₂ in the same time. At higher temperature, particles have more energy and collide more frequently and with greater energy, increasing the rate of reaction.
Common mistakes: Calculating rates using total volume not change in volume.; Mixing up rates at different temperatures.; Confusing why temperature affects rate.
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Marking points
M1 (a(i)) · 1 mark · Correctly identifies the change in volume of CO₂ over first 2 minutes at 20°C: 27 cm³.
M2 (a(i)) · 1 mark · Divides volume by time to obtain correct average rate: 27 cm³ ÷ 2 min = 13.5 cm³/min.
M3 (a(ii)) · 1 mark · States that the rate is higher at 40°C based on greater volume of CO₂ in a fixed time.
M4 (a(ii)) · 1 mark · Mentions more frequent (or more energetic) collisions at higher temperature.
M5 (a(ii)) · 1 mark · Explains that higher temperature increases particle speed, so more successful collisions occur each second.
Worked solution
a(i) At 20°C, the volume of CO₂ collected in the first 2 minutes is 27 cm³.
a(ii) The rate of reaction at 40°C is greater than at 20°C, as shown by the higher volume of CO₂ produced in the same time (e.g., 60 cm³ at 40°C after 2 min, compared to 27 cm³ at 20°C).
At higher temperature, the particles move faster and collide more often and with more energy. This increases the number of successful collisions per second, so the rate of reaction increases.