Chemistry 9701 · AS & A Level · Reaction kinetics

Reaction kinetics — practice question

Ethanal, $\text{CH}_3\text{CHO}$, forms a dimer in alkaline solution according to the equation below. $2\text{CH}_3\text{CHO} \rightarrow \text{CH}_3\text{CH(OH)CH}_2\text{CHO}$ The initial rate of this reaction was measured using different concentrations of $\text{CH}_3\text{CHO}$ and $\text{OH}^-$.
(a(i))[1]

Deduce the reaction order with respect to $\text{CH}_3\text{CHO}$.

(a(ii))[1]

Deduce the reaction order with respect to $\text{OH}^-$.

(a(iii))[1]

State the overall rate equation for this reaction.

(a(iv))[1]

State the units for the rate constant, $k$.

(a(v))[1]

Calculate the relative initial rate for a reaction in which $[\text{CH}_3\text{CHO}]$ is $0.30\,\text{mol dm}^{-3}$ and $[\text{OH}^-]$ is $0.030\,\text{mol dm}^{-3}$.

(b(i))[2]

A three-step mechanism has been proposed for the reaction in (a). Using your rate equation in (iii), predict which step is the rate-determining one. Explain your answer.

(b(ii))[1]

Describe the chemical behaviour of $\text{CH}_3\text{CHO}$ in step 1.

(c)[1]

Name the mechanism occurring in steps 2 and 3.

(d)[2]

Using the diagram below, show the mechanism for step 2, including the relevant curly arrows and dipoles.

Worked solution & mark scheme

This 11-mark question has a full step-by-step worked solution and mark scheme. One marking point: First-order

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