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CAIE A-Level Chemistry 26.1.4 Rate Constant Calculations

Practise calculating k from an experimental rate law or first-order half-life and determining its units.

Syllabus
2028–2030
Course
Chemistry 9701
Level
A2

Exam points

  • rearrange the experimentally determined rate equation and substitute one complete initial-rate run
  • for a first-order reaction use k = 0.693/t1/2 with time in the required unit
  • derive k units by dividing rate units by concentration units raised to the overall order

26.1.4—The numerical value of a rate constant, e.g question 1

[Maximum number: 2]

A and B react together to give product AB .

A+B→ABA+B \rightarrow A B

When the concentrations of A and B are both 0.0100moldm−30.0100 \mathrm{moldm}^{-3}, the rate of formation of AB is 7.62×10−4moldm−3 s−17.62 \times 10^{-4} \mathrm{moldm}^{-3} \mathrm{~s}^{-1}. When the concentrations of A and B are both 0.0200moldm−30.0200 \mathrm{moldm}^{-3}, the rate of formation of AB is 3.05×10−3moldm−3 s−13.05 \times 10^{-3} \mathrm{moldm}^{-3} \mathrm{~s}^{-1}.

Choose one of the rate equations you have written in (i), and calculate the value of the rate constant, k. Include the units of k.
k= units

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