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Rate equation and rate constant

Rate equations
AQA 7405
ORIGINAL

rate = k[A]m[B]n

Orders come from rate data, not balancing coefficients, and k units follow from the final rate equation.

Board and spec code confirmed against AQA 7405 · registry checked 2026-07-11How this checking works

Work it, then mark it

Do each calculation on paper first, then reveal the mark scheme and tick the marks you actually earned — the same way you should mark past papers.

Q1

Doubling [A] while [B] is constant makes rate four times larger. Doubling [B] while [A] is constant has no effect. When [A] = 0.200 mol/dm3, rate = 0.0360 mol/dm3/s. Deduce the rate equation and calculate k with units.

[4 marks]

Total for this question: 4

Do the calculation on paper first — then mark it.

Where the marks get lost

  • Reading reaction orders from the balanced equation.
  • Quoting k without deriving its units from rate divided by concentration powers.

Exam tip: Compare pairs where only one concentration changes, then substitute into the completed rate equation.

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