CIE Nov 2016 v2 Paper 2 Q2

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Dinitrogen tetraoxide, N2O4, and nitrogen dioxide, NO2, exist in dynamic equilibrium with each other. PMT The energy profile for this reaction is shown. N2O4(g) 2NO2(g) H = +54 kJ mol1 energy N2O4(g) 2NO2(g) reaction pathway (a) Add labelled arrows to the energy profile to indicate the enthalpy change of the reaction, H, the activation energy of the forward reaction, Ea. [2] (b) 0.0500 mol of N2O4 was placed in a sealed vessel of volume 1.00 dm3, at a temperature of 50 C and a pressure of 1.68105 Pa. The mass of the resulting equilibrium mixture was 4.606 g. (i) Calculate the average molecular mass, Mr, of the resulting equilibrium mixture. Give your answer to three significant figures. (ii) The number of moles of N2O4 that dissociated can be represented by n. State, in terms of n, the amount, in moles, of NO2 in the equilibrium mixture. Mr =[2]UCLES 2016 9701/22/O/N/16 moles of NO2 =[1]<br /> The number of moles of N2O4 remaining at equilibrium is (0.05n). (iii) State, in terms of n, the total amount, in moles, of gas in the equilibrium mixture. (iv) State, in terms of n, the mole fraction of NO2 in the equilibrium mixture. PMT [1] [1] In this equilibrium mixture, the mole fraction of NO2 is 0.400. (v) Use your answers to (ii) and (iv) to calculate the amount in moles of each gas in the equilibrium mixture. Give your answers to three significant figures. amount of N2O4 =mol amount of NO2 =mol [2] (vi) Write the expression for the equilibrium constant, Kp, for this equilibrium. Kp = (vii) Use the total pressure of the mixture, 1.68105 Pa, to calculate the value of the equilibrium constant, Kp, and give its units. [1]UCLES 2016 9701/22/O/N/16 Kp =units =[3] [Total: 13] [Turn over<br />

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