Ethanal, CH3CHO, reacts with nitrogen dioxide, NO2. The products of the first step of this reaction are a CH3C=O radical and a molecule of nitrous acid, HNO2. CH3CHO + NO2 → CH3C=O + HNO2

1. (a)(i)Use two words to complete the sentence. This reaction involves covalent bond between a hydrogen atom and a carbon atom in CH3CHO.[1]
2. (a)(ii)The hydrogen atom mentioned in (a)(i) forms a covalent bond with one of the oxygen atoms of an NO2 molecule. An NO2 molecule has a single, unpaired electron on the nitrogen atom. All electrons are paired in an HNO2 molecule. Draw dot-and-cross diagrams of NO2 and HNO2 in the boxes. Show outer shell electrons only.[1]
3. (a)(iii)Use VSEPR theory to predict the bond angle at the nitrogen atom in an HNO2 molecule. bond angle =[1]
4. (b)The rate equation for the reaction between CH3CHO and NO2 is shown. rate = k[CH3CHO][NO2] Under certain conditions, when the concentrations of both CH3CHO and NO2 are 0.200 mol dm–³, the rate of the reaction is 1.53 × 10–4 mol dm–³ s–1. Calculate the value of the rate constant, k, under these conditions. Give the units of k. k = units[2]
5. (c)The reaction mixture described in (b) is monitored over a period of time. Predict whether the graph of [NO2] against time shows a constant half-life. Explain your answer. prediction explanation[1]
6. (d)NO2 also reacts with ozone, O3. The rate equation is shown. rate = k₁[NO2] Under certain conditions, the value of k₁ is 0.0848 s–1. The reaction has a constant half-life under these conditions. Calculate the half-life in seconds. half-life = s[1]
7. (e)NO2 is present in the exhaust gases of cars. It can react with carbon monoxide, CO, on the surface of a heterogeneous catalyst in the car's catalytic converter. Describe the mode of action of this heterogeneous catalyst.[2]