OCR A Jun 2014 Paper 2 Q3

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3 Hydrogen iodide, HI, is a colourless gas that can be made from the reaction of hydrogen, H2, and iodine, I2. This reversible reaction is shown in equilibrium 3.1 below. H2(g) + I2(g) 2HI(g) H = 9 kJ mol1 equilibrium 3.1 The activation energy for the forward reaction is 173 kJ mol1. (a) Complete the enthalpy profile diagram below for the forward reaction in equilibrium 3.1. On your diagram:Label the activation energy, Ea Label the enthalpy change of reaction, H Include the formulae of the reactants and products. enthalpy progress of reaction [2] (b) Calculate the activation energy, Ea, for the reverse reaction. Ea (reverse reaction) =kJ mol1 [1] (c) When the reverse reaction takes place hydrogen iodide, HI, decomposes to form iodine and hydrogen. Calculate the enthalpy change when 336 dm3 of hydrogen iodide, measured at room temperature and pressure, decomposes. Include the sign for enthalpy change in your answer.OCR 2014 enthalpy changekJ [2]<br />
 (d) A student mixes hydrogen and iodine at room temperature and pressure and allows the mixture to reach dynamic equilibrium. H2(g) + I2(g) 2HI(g) H = 9 kJ mol1 equilibrium 3.1 (i) A closed system is required for dynamic equilibrium to be established. State one other feature of this dynamic equilibrium.[1] (ii) The student heats the equilibrium mixture keeping the volume constant. Predict how the composition of the equilibrium mixture changes on heating. Explain your answer.[2] (iii) Predict and explain what effect, if any, an increase in the pressure would have on the position of the equilibrium. effectexplanation[1] (e) Calculate the bond enthalpy for the HI bond in equilibrium 3.1, given the following information. Bond HH II Bond Enthalpy / kJ mol1 436 151OCR 2014 bond enthalpykJ mol1 [2] [Total: 11] Turn over<br />

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