Turn over 23 9 This question is about lattice energies. (a) The table shows the theoretical and experimental lattice energy values of two compounds. Compound Theoretical lattice energy / kJ mol–1 Experimental lattice energy / kJ mol–1 magnesium iodide –1944 –2327 barium iodide –1831 –1877 (i) State what can be deduced by the close similarity of the lattice energy values for barium iodide. (1) .................................................................................................................................................................................................................................................................................... .................................................................................................................................................................................................................................................................................... (ii) Explain why there is a significant difference in the lattice energy values for magnesium iodide. 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Label Energy change Value / kJ mol–1 A standard enthalpy change of atomisation of copper +338 B standard enthalpy change of atomisation of oxygen +249 C sum of first and second ionisation energies of copper +2704 D first electron affinity of oxygen –141 E second electron affinity of oxygen +798 F standard enthalpy change of formation of copper(II) oxide –157 (i) Complete the diagram of the Born‑Haber cycle for copper(II) oxide. Include labels of enthalpy changes with arrows indicating the direction of change, and the respective species with state symbols. (4) Cu(s) + ½O2(g) F CuO(s) Turn over 25 (ii) Calculate the lattice energy of copper(II) oxide. (1) (c) A different energy cycle can be used to calculate lattice energy. Ca2+(g) + 2Br–(g) CaBr2(s) Ca2+(aq) + 2Br–(aq) Enthalpy change Value / kJ mol–1 enthalpy change of solution of CaBr2 –73 enthalpy change of hydration of Ca2+ –1577 enthalpy change of hydration of Br– –336 Calculate the lattice energy of calcium bromide. (2) (Total for Question 9 = 12 marks) 26 10 * A student wrote: Whether or not a reaction occurs depends only on the thermodynamic feasibility calculated using ∆G = ∆H — T∆Ssystem Discuss this statement. Include reference to:  changes in the values and signs of the terms in the equation for both endothermic and exothermic reactions  circumstances where a reaction that is predicted to be thermodynamically feasible may not occur in practice. 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(Total for Question 10 = 6 marks) TOTAL FOR PAPER = 90 MARKS 28