OCR A Jun 2013 Paper 5 Q3

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3 Hydrogen and iodine react together in a reversible reaction: H2(g) + I2(g) 2HI(g) H = 9 kJ mol1 A chemist mixes together 2.00103 mol H2(g) and 4.00103 mol I2(g) in a 1.00 dm3 container. The chemist seals the container. The mixture is heated and left to reach equilibrium. At equilibrium, the mixture contains 3.00104 mol of H2. (a) Calculate the equilibrium constant, Kc, including units, if any, for this equilibrium. Give your answer to three significant figures. Kc =units[5]OCR 2013<br /> (b) The chemist repeats the experiment several times. In each experiment, the chemist makes one change. (i) The chemist uses 3.00103 mol H2(g) instead of 2.00103 mol H2(g). Predict whether the amounts of H2(g), I2(g) and HI(g) in the equilibrium mixture would be greater, smaller or the same as in the original experiment. Answer by placing ticks in the appropriate boxes of the table below. H2(g) I2(g) HI(g) Greater Smaller The same [2] (ii) The chemist heats the mixture to a higher temperature at constant pressure. Explain whether the value of Kc would be greater, smaller or the same.[1] (iii) The chemist increases the pressure of the mixture at constant temperature. Explain whether the value of Kc would be greater, smaller or the same.[1] [Total: 9]OCR 2013 Turn over<br />

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