Nitrogen monoxide, NO, reacts with ozone, O₃. NO(g) + O₃(g) → NO₂(g) + O₂(g) This reaction is first order with respect to both NO and O₃. At 298 K, the rate constant k = 11500 mol⁻¹ dm³ s⁻¹.

1. (a)(i)Complete the rate equation for this reaction. rate = ......................................................................................................................................... [1][1]
2. (a)(ii)A reaction is carried out in which the initial concentrations of NO and O₃ are both 1.20 × 10⁻⁶ mol dm⁻³. Calculate the initial rate of the reaction. State its units. rate of reaction = .............................................. units = .............................................. [2][2]
3. (a)(iii)The reaction described in (a)(ii) is monitored over a period of time. Predict whether or not the graph of [NO] against time, under these conditions, shows that the reaction has a constant half-life. Explain your answer. prediction .................................................................................................................................... explanation .................................................................................................................................... [1][1]
4. (b)Nitrous oxide, N₂O, decomposes into its elements. 2N₂O(g) → 2N₂(g) + O₂(g) At a high temperature, a small amount of platinum wire is added to a large amount of nitrous oxide. The reaction follows zero order kinetics. The platinum wire behaves as a catalyst.
5. (b)(i)Sketch a graph, on the axes below, of reaction rate against time for the catalysed decomposition of N₂O under these conditions. reaction rate time [1][1]
6. (b)(ii)Sketch a graph, on the axes below, of [N₂O] against time for this reaction. [N₂O] time [1][1]
7. (b)(iii)Platinum behaves as a heterogeneous catalyst in this reaction. Describe the mode of action of a heterogeneous catalyst. [3][3]
8. (b)(iv)Suggest a reason why this reaction has zero order kinetics when the amount of nitrous oxide is large and the amount of platinum is small. [1][1]

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