Dinitrogen pentoxide, N₂O₅, is dissolved in an inert solvent (solv) and the rate of decomposition of N₂O₅ is investigated. This reaction produces nitrogen dioxide, which remains in solution, and oxygen gas. N₂O₅(solv) → 2NO₂(solv) + ½O₂(g)

1. (a)Suggest what measurements could be used to follow the rate of this reaction from the given information.[1]
2. (b)(i)In a separate experiment, the rate of the decomposition of N₂O₅(g) is investigated. N₂O₅(g) → 2NO₂(g) + ½O₂(g) The graph shows the results obtained. [Figure showing a graph of [N₂O₅] /mol dm⁻³ vs time/s] The reaction is first order with respect to N₂O₅. This can be confirmed from the graph using half-lives. Explain the term half-life of a reaction.[1]
3. (b)(ii)Determine the half-life of this reaction. Show your working on the graph. half-life = s[1]
4. (b)(iii)Suggest the effect on the half-life of this reaction if the initial concentration of N₂O₅ is halved.[1]
5. (c)(i)Use the graph in 5(b) to determine the rate of reaction at 200 s. Show your working. rate = units[2]
6. (c)(ii)The rate equation for this reaction is shown. rate = k[N₂O₅] Use your answer to (c)(i) to calculate the value of the rate constant, k, for this reaction and state its units. k = units[1]
7. (d)Nitrogen dioxide reacts with ozone, O₃, as shown. 2NO₂ + O₃ → N₂O₅ + O₂ The rate equation for this reaction is rate = k[NO₂][O₃]. Suggest a possible two-step mechanism for this reaction.[2]

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