Edexcel IAL Chemistry Changing the Subject

Practise Edexcel IAL Chemistry changing the subject of an equation by rearranging rate expressions to calculate rate constants with matching units.

Exam points

Rearrange a rate equation to make k the subject, then calculate its value and units from experiment data.

[Maximum number: 2]

This question is about the reaction between nitrogen monoxide and oxygen.

\mathrm{NO}(\mathrm{~g})+1 / 2 \mathrm{O}_{2}(\mathrm{~g}) \rightleftharpoons \mathrm{NO}_{2}(\mathrm{~g})

The results of a series of kinetics experiments are shown.

Table for Question B.2.2—Changing the subject of an equation question 1 — Edexcel A-Level Chemistry A2

The data for experiments 1-5 were plotted on a graph.

Figure for Question B.2.2—Changing the subject of an equation question 1 — Edexcel A-Level Chemistry A2

Calculate the rate constant for this reaction using the data from experiment 1 and your rate equation. Include units in your answer.

substitution or rearrangement

- answer and units

Example of a calculation:
$\begin{aligned} 0.040=\mathrm{k}(0.010)^{2}(0.05) \mathrm{k}=\frac{0.040}{(0.010)^{2}(0.05)} \end{aligned}$ $=8000 \mathrm{dm}^{6} \mathrm{~mol}^{-2} \mathrm{~s}^{-1}$
Allow units in any order
Allow $\mathrm{s}^{-}$
Allow $\mathrm{dm}^{6} / \mathrm{mol}^{2} \mathrm{~s}$ but not $\mathrm{dm}^{6} / \mathrm{mol}^{2} / \mathrm{s}$
Allow TE on a(iv) for both marks, units must match
order for M2
Correct answer with units scores 2, even if expression
in Q18(a)(iv) is incorrect

(2)

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B.2.2—Changing the subject of an equation question 1