Fluorine reacts with chlorine dioxide, ClO2, as shown. F2(g) + 2ClO2(g) → 2FClO2(g) The rate of the reaction is first order with respect to the concentration of F₂ and first order with respect to the concentration of ClO2. No catalyst is involved.

1. (a)(i)Suggest a two-step mechanism for this reaction. step 1 step 2[2]
2. (a)(ii)Identify the rate-determining step in this mechanism. Explain your answer.[1]
3. (b)When the rate of the reaction is measured in moldm⁻³s⁻¹ the numerical value of the rate constant, k, is 1.22 under certain conditions.
4. (b)(i)Complete the rate equation for this reaction, stating the overall order of the reaction. rate = overall order of reaction =[1]
5. (b)(ii)Use your rate equation in (i) to calculate the rate of the reaction when the concentrations of F2 and ClO2 are both 2.00 × 10⁻³moldm⁻³. rate =[1]
6. (c)Under different conditions, and in the presence of a large excess of ClO2, the rate equation is as shown. rate = k₁[F2] The half-life, t½, of the concentration of F2 is 4.00 s under these conditions.
7. (c)(i)Calculate the numerical value of k₁, giving its units. Give your answer to three significant figures. k₁ = units[2]
8. (c)(ii)An experiment is performed under these conditions in which the starting concentration of F2 is 0.00200 mol dm⁻³. Draw a graph on the grid in Fig. 1.1 to show how the concentration of F2 changes over the first 12s of the reaction.[1]
9. (c)(iii)Use your graph in Fig. 1.1 to find the rate of the reaction when the concentration of F₂ is 0.00100 moldm⁻³. Show your working on the graph. rate[1]

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