CIE Mar 2017 v2 Paper 4 Q4

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(a) Chlorine dioxide undergoes the following reaction in aqueous solution. 2Cl O2 + 2OH Cl O2+ Cl O3+ H2O PMT The initial rate of the reaction was measured at different initial concentrations of Cl O2 and OH. The table shows the results obtained. experiment 1 2 3 [Cl O2] / mol dm3 1.25102 2.50102 2.50102 [OH] / mol dm3 1.30103 1.30103 2.60103 initial rate / mol dm3 s1 2.33104 9.34104 1.87103 (i) Use the data in the table to determine the rate equation, showing the order with respect to each reactant. Show your reasoning.rate equation =[3] (ii) Calculate the value of the rate constant, k, using the data from experiment 2. State its units. k =units[2] (b) (i) Explain the difference between heterogeneous and homogeneous catalysts.[1]UCLES 2017 9701/42/F/M/17<br /> (ii) Complete the table using ticks () to indicate whether the catalyst used in the reaction is heterogeneous or homogeneous. catalysed reaction heterogeneous homogeneous PMT manufacture of ammonia in the Haber process removal of nitrogen oxides from car exhausts oxidation of sulfur dioxide in the atmosphere [2] (c) Some reactions are catalysed by one of the products of the reaction. This is called autocatalysis. An example of autocatalysis is the reaction between acidified manganate(VII) ions, MnO4 , and ethanedioic acid, (CO2H)2. Mn2+ ions catalyse this reaction. The reaction is slow in the absence of a catalyst. (i) Balance the equation for this reaction. MnO4+ H+ + (CO2H)2 Mn2+ + CO2 + H2O [2] (ii) The graph shown is a concentration-time graph for a typical reaction. concentration of reactant On the axes below, sketch the curve you would expect for the autocatalysed reaction in (i). time concentration of MnO4 timeUCLES 2017 9701/42/F/M/17 [2] [Turn over<br /> (d) (i) Describe, with the aid of a reaction pathway diagram, the effect of a catalyst on a reversible reaction. Suggest why catalysts are used in industrial processes. 10 PMT[3] (ii) The reaction for the Haber process to produce ammonia is shown. N2(g) + 3H2(g) 2NH3(g) H o = 92 kJ mol1 At 500 C, when pressure is measured in atmospheres, the numerical value of Kp for this equilibrium is 1.45105. Write the expression for Kp for this equilibrium. Kp = Calculate the partial pressure of NH3 at equilibrium at 500 C, when the partial pressure of N2 is 20 atm and that of H2 is 60 atm. pNH3 =atm [2] [Total: 17]UCLES 2017 9701/42/F/M/17<br />

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