Three experiments are carried out to investigate the reaction of nitrogen oxide, NO, with chlorine. 2NO + Cl2 → 2NOCI The rate equation for this reaction is shown. rate = k[NO]²[Cl2]

1. (a)(i)Under the conditions used in experiments 1 and 2, the value of k is 26.4. The rate of the reaction is measured in moldm⁻³s⁻¹. State the units of k. units of k = .........................................................[1]
2. (a)(ii)In experiment 1, the initial concentrations of NO and Cl2 are equal. The initial rate of the reaction in experiment 1 is 2.57 × 10⁻⁶ moldm⁻³s⁻¹. Calculate the initial concentration of NO. Show your working. initial concentration of NO = ..............................................moldm⁻³[2]
3. (a)(iii)In experiment 2, the initial concentrations of NO and Cl2 are both ten times greater than the initial concentrations used in experiment 1. Calculate the initial rate of the reaction in experiment 2. initial rate of reaction in experiment 2 = ........................................moldm⁻³s⁻¹[1]
4. (b)(i)Experiment 3 uses a large excess of NO. The initial concentration of Cl2 is 2.00 × 10⁻⁴ moldm⁻³. The graph of [Cl2] against time shows that the reaction has a constant half-life, t½· Explain this observation.[1]
5. (b)(ii)Under the conditions used in experiment 3, the value of the rate constant is 105.6. Show that t½ of [Cl2] is 6.56 × 10⁻³s under these conditions.[1]
6. (b)(iii)Calculate the time taken, in s, for [Cl2] to fall to 1.25 × 10⁻⁵moldm⁻³ in experiment 3. time = .................................s[1]
7. (c)Sulfur dioxide, SO2, reacts very slowly with oxygen in the atmosphere, forming sulfur trioxide, SO3. This reaction is much faster in the presence of NO. Explain the role of NO in this process. Include chemical equations in your answer.[3]