CIE Nov 2015 v3 Paper 5 Q2

Answers available below

At 25 C, dinitrogen tetroxide, N2O4(g), forms an equilibrium mixture with nitrogen dioxide, NO2(g). PMT N2O4(g) 2NO2(g) H = +57.2 kJ mol1 As N2O4(g) is colourless and NO2(g) is brown, the composition of an equilibrium mixture can be determined by its colour. (a) Write an expression for the equilibrium constant, Kc, for this equilibrium. [1] (b) In an experiment, quantities of N2O4 are left to reach an equilibrium which contains N2O4 and NO2. These are analysed to determine the concentrations of N2O4(g) and NO2(g) that are present. The results are listed in therst two columns of the table below. Complete the third column of the table to give the value of [NO2(g)]2 for each of the results of the experiment. Values should be given to three signi cantgures. [N2O4(g)] / mol dm3 [NO2(g)] / mol dm3 [NO2(g)]2 / mol2 dm6 0.900 0.800 0.700 0.600 0.500 0.400 0.300 0.200 0.100 0.0729 0.0687 0.0643 0.0595 0.0548 0.0486 0.0390 0.0344 0.0243 [2] (c) (i) The value of the equilibrium constant for N2O4(g) graph of [N2O4(g)] against [NO2(g)]2. 2NO2(g) can be calculated from a Use the grid on page 7 to plot this graph and draw a line of bestt through the plotted points.UCLES 2015 9701/53/O/N/15<br /> 6m d 2 l o m / 2 ] ) g ( 2 O N PMT 0.006 0.005 0.004 0.003 0.002 0.001 0.000 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 [N2O4(g)] / mol dm3UCLES 2015 9701/53/O/N/15 [2] [Turn over<br /> (ii) Choose two suitable sets of values from your graph and use them to calculate a value for the equilibrium constant, Kc. Give your answer to three signi cantgures and give its units. co-ordinates of two points usedPMT Kc =units[3] (d) Identify the result which is most anomalous and suggest a reason, other than a calculation error, why this may have occurred.[2] (e) (i) On your graph, draw a line that would be obtained if the temperature of the equilibrium mixture was raised. [1] (ii) Explain the position of the line drawn in (i).[1] (iii) What effect, if any, would the higher temperature have on the value of Kc?[1] (iv) How would your value for the equilibrium constant change if the pressure applied to the equilibrium mixture was increased?[1]UCLES 2015 9701/53/O/N/15<br /> (f) In the experiments, the results have been obtained by starting with pure N2O4(g) and then letting the equilibrium with NO2(g) form. Calculate the starting concentration of pure N2O4(g) that would be required to produce the mixture of 0.900 mol dm3 of N2O4(g) and 0.0729 mol dm3 of NO2(g) once equilibrium had been established. PMT [1] [Total: 15]UCLES 2015 9701/53/O/N/15 [Turn over<br />

Show answer