OCR A Jan 2011 Paper 5 Q1

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Answer all the questions. 1 Hydrogen, H2, reacts with nitrogen monoxide, NO, as shown in the equation below. 2H2(g) + 2NO(g) N2(g) + 2H2O(g) A chemist carries out a series of experiments and determines the rate equation for this reaction: (a) In one of the experiments, the chemist reacts together: rate = k[H2(g)][NO(g)]21.2102 mol dm3 H2(g) 6.0103 mol dm3 NO(g) The initial rate of this reaction is 3.6102 mol dm3 s1. Calculate the rate constant, k, for this reaction. State the units, if any. (b) Predict what would happen to the initial rate of reaction for the following changes in concentrations. k =units[3] (i) The concentration of H2(g) is doubled.[1] (ii) The concentration of NO(g) is halved.[1] (iii) The concentrations of H2(g) and NO(g) are both increased by four times.[1]OCR 2011<br /> (c) The chemist carries out the reaction between hydrogen and nitrogen monoxide at a higher pressure. (i) Explain, with a reason, what happens to the initial rate of reaction.[1] (ii) State what happens to the rate constant.[1] (d) This overall reaction between hydrogen and nitrogen monoxide takes place by a two-step mechanism. The first step is much slower than the second step. Suggest a possible two-step mechanism for the overall reaction. step 1:step 2:[2] [Total: 10]OCR 2011 Turn over<br />

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