OCR A Jun 2013 Paper 5 Q2

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In aqueous solution, benzenediazonium chloride, C6H5N2Cl, decomposes above 10 C. C6H5N2Cl(aq) + H2O(l) C6H5OH(aq) + N2(g) + HCl(aq) A student investigates the rate of this reaction using an excess of water at 50 C. The student takes measurements at intervals during the reaction and then plots his experimental results to give the graph shown below. [C6H5N2Cl (aq)] / mol dm3 6.0 5.0 4.0 3.0 2.0 1.0 20 40 60 80 100 120 140 160 180 time / s (a) The student uses half-life to suggest the order of reaction with respect to C6H5N2Cl. (i) What is meant by the half-life of a reaction?[1] (ii) Confirm the order of reaction with respect to C6H5N2Cl. Show your working on the graph.[2]OCR 2013<br />
 (iii) What would be the effect, if any, on the half-life of this reaction of doubling the initial concentration of C6H5N2Cl ?[1] (b) The student predicts that the rate equation is: rate = k [C6H5N2Cl]. (i) Using the graph and this rate equation, determine the rate of reaction after 40 s. Show your working on the graph. (ii) Calculate the rate constant, k, for this reaction and give its units. rate = units[3] k =units[2] (c) The order of this reaction with respect to H2O is effectively zero. Explain why.[1] [Total: 10]OCR 2013 Turn over<br />

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