Chemistry 9701 · AS & A Level · Reaction kinetics

Reaction kinetics — practice question

(a)[2]

Explain what is meant by each of the following terms: half-life of a reaction rate-determining step

(b)[4]

The reaction between hydroxide ions and bromomethane is first order with respect to $[\text{OH}^-]$ and first order with respect to $[\text{CH}_3\text{Br}]$. $\text{CH}_3\text{Br} + \text{OH}^- \rightarrow \text{CH}_3\text{OH} + \text{Br}^-$ Suggest a practical procedure that would confirm that the reaction is first order with respect to $[\text{OH}^-]$. Your procedure should give details of the measurements that would be made so that the reaction rate can be calculated. You should also include a way of displaying the data to show that the reaction is first order with respect to $[\text{OH}^-]$.

(c)[3]

The hydrolysis of methyl ethanoate, $\text{CH}_3\text{CO}_2\text{CH}_3$, by hydroxide ions, $\text{OH}^-$, is first order with respect to $[\text{CH}_3\text{CO}_2\text{CH}_3]$ and also first order with respect to $[\text{OH}^-]$. In one experiment, • $[\text{CH}_3\text{CO}_2\text{CH}_3] = 0.100\ \text{mol dm}^{-3}$ • $[\text{OH}^-] = 0.100\ \text{mol dm}^{-3}$ • rate of reaction $= 2.06 \times 10^{-3}\ \text{mol dm}^{-3}\text{ s}^{-1}$ Write a rate equation for this reaction and calculate the value of the rate constant, $k$, under these conditions. State the units of $k$.

Worked solution & mark scheme

This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: The time needed for the amount/concentration of a reactant to fall by half

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