Question detail
What is the formula to calculate the rate of a reaction?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
AS practical skills and required practical activities
Question
- A. Rate = change in quantity / time
- B. Rate = time / change in quantity
- C. Rate = quantity / time
- D. Rate = change in time / quantity
Answer
Rate = change in quantity / time
Explanation
The correct option is Rate = change in quantity / time. Rate = change in quantity / time is the best answer because it directly supports the AQA A-Level Chemistry objective to measure reaction rates using appropriate methods. This reasoning is anchored to AS apparatus and techniques in AS practical skills and required practical activities, and it separates rates from similar A-Level ideas rather than relying on a vague recall statement. Other options are weaker if they use the wrong evidence, calculation, mechanism, observation, unit, or conclusion for this subtopic.
Common mistake
Incorrect Measurement of Reaction Rate
Students often confuse the method of measuring reaction rates, leading to incorrect calculations. For example, they might use the total time taken for a reaction instead of the change in concentration over time.
To accurately measure reaction rates, use the formula: rate = change in concentration / time. For instance, if the concentration of a reactant decreases from 0.5 mol/dm³ to 0.2 mol/dm³ in 10 seconds, substitute into the formula: rate = (0.5 - 0.2) mol/dm³ / 10 s = 0.03 mol/dm³/s. This shows the correct method for calculating the reaction rate.
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