OCR A Jun 2012 Paper 5 Q2

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2 A chemist carries out an investigation on the equilibrium system shown below. 2CO(g) + 2NO(g) 2CO2(g) + N2(g) H = 788 kJ mol1 The chemist mixes 0.46 mol of CO with 0.45 mol of NO. The mixture is left to reach equilibrium at constant temperature. The student analyses the equilibrium mixture and finds that 0.25 mol NO remains. The total volume of the equilibrium mixture is 1.0 dm3. (a) (i) Write the Kc expression for this equilibrium. (ii) What are the units of this equilibrium constant?[1] [1] (iii) Determine the value of Kc for this equilibrium mixture. Show all your working. Kc =[4]OCR 2012<br />
 (iv) What does your value of Kc suggest about the position of equilibrium in this experiment?[1] (b) The chemist increases both the temperature and the pressure of the equilibrium mixture. The mixture is left to reach equilibrium again. (i) What is the effect, if any, on the value of Kc? Explain your answer.[1] (ii) Explain why it is difficult to predict what would happen to the position of equilibrium after these changes in temperature and pressure.[2] [Total: 10]OCR 2012 Turn over<br />

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