Experiments to measure the rate of reaction
4 marks · Normal| Time / min | Mass of CO2 lost / g |
|---|---|
| 0 | 0.00 |
| 1 | 0.32 |
| 2 | 0.54 |
| 3 | 0.63 |
| 4 | 0.66 |
| 5 | 0.67 |
Calculate the average rate of reaction between 0 and 2 minutes (give your answer in g/min).
Calculate the average rate of reaction between 2 and 5 minutes (give your answer in g/min).
State and explain the main trend in the rate of reaction as time increases.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) 0.27 g/min · must show correct calculation: (0.54-0.00)/2
(b) 0.043 g/min · must show correct calculation: (0.67-0.54)/3
(c) The rate of reaction decreases as time increases, because the reactants are being used up and so there are fewer collisions between particles. · must show states rate decreases with time, explains reason using reactant use/concentration/collisions
Common mistakes: confuses end and start values
Show mark scheme and worked solution
Marking points
A1 (a) · 1 mark · Correctly calculates average rate from 0–2 min: (0.54−0.00)/2 = 0.27 g/min
A2 (b) · 1 mark · Correctly calculates average rate from 2–5 min: (0.67−0.54)/3 = 0.043 g/min
B1 (c) · 1 mark · States there is a decrease in rate of reaction as time goes on.
M1 (c) · 1 mark · Explains the trend using reactant use or concentration decrease, or collision theory.
Worked solution
a) Average rate (0–2 min) = (0.54−0.00)/2 = 0.27 g/min b) Average rate (2–5 min) = (0.67−0.54)/3 = 0.13/3 = 0.043 g/min c) The rate of reaction decreases over time because the acid is used up, so fewer reactant particles are available for collisions.