Chemistry 9701 · AS & A Level · Reaction kinetics

Reaction kinetics — practice question

In aqueous solution, iron(III) ions react with iodide ions, as shown: $2\text{Fe}^{3+} + 2\text{I}^- \rightarrow 2\text{Fe}^{2+} + \text{I}_2$. Table 4.1 shows a set of experiments carried out with different concentrations of $\text{Fe}^{3+}$ and $\text{I}^-$.
(a(i))[1]

Explain what the term overall order of reaction means.

(a(ii))[2]

Use the information in Table 4.1 to work out the order of reaction with respect to $\text{Fe}^{3+}$ and with respect to $\text{I}^-$. Explain how you reached your conclusion.

(a(iii))[1]

Use your answer to a(ii) to construct the rate equation for this reaction.

(a(iv))[2]

Use your answer to a(iii) and the data from experiment 1 to calculate the rate constant, $k$, for this reaction. Include the units of $k$.

(a(v))[1]

Describe qualitatively the effect of an increase in temperature on the rate constant and on the rate of this reaction.

(b(i))[1]

Suggest which of the steps, 1, 2, 3 or 4, in this mechanism is the rate-determining step. Explain your answer.

(b(ii))[1]

Identify a step in Fig. 4.1 that involves a redox reaction. Explain your answer in terms of oxidation numbers.

(b(iii))[1]

Suggest the role of HIO in this mechanism. Explain your reasoning.

Worked solution & mark scheme

This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Overall order is the total of the powers of the concentrations in the rate equation” …

  • Full mark scheme, point by point
  • Step-by-step worked solution
  • Write your answer & get it marked instantly by AI