CIE Mar 2016 v2 Paper 4 Q2

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(a) Calcium metal reacts with chlorine gas to form calcium chloride, CaCl 2. PMT (i) Write an equation, including state symbols, to represent the lattice energy of calcium chloride, CaCl 2.[1] (ii) Complete a fully labelled Born-Haber cycle that could be used to calculate the lattice energy, ,for calcium chloride. Ca(s) + Cl 2(g) CaCl 2(s) [2] (iii) Use your answer to (ii) and the following data, together with relevant data from the Data Booklet, to calculate a value for for calcium chloride. standard enthalpy change of formation of CaCl 2(s), standard enthalpy change of atomisation of Ca(s), electron affinity of chlorine atoms 796 kJ mol1 +178 kJ mol1 349 kJ mol1 =kJ mol1 [3] (b) Entropy is a measure of the disorder of a system. Describe and explain what happens to the entropy of a gas when the temperature is increased.[2]UCLES 2016 9701/42/F/M/16<br /> PMT (c) The table shows four reactions. (i) For each reaction, predict the sign of the entropy change, S o. If you predict no entropy change, write no change in the table below. The first one has been done for you. reaction CO(g) + O2(g)CO2(g) 1 O2(g)MgO(s) Mg(s) + 2 sign of S o negative CuSO4(s) + 5H2O(l)CuSO4.5H5O(s) NaHCO3(s) + H+(aq)Na+(aq) + CO2(g) + H2O(l) (ii) Explain why the entropy change for the first process is negative.[1] [2] (d) Calculate the standard entropy change, S o, for this reaction. N2(g) + 3H2(g)2NH3(g) Standard entropies, S o, in J K1 mol1 are given. N2(g) +192 H2(g) +131 NH3(g) +193 S oJ K1 mol1 [2] (e) Whether or not a chemical reaction is spontaneous (feasible) can be deduced by calculating the change in free energy, G o, at a given temperature. MgCO3(s)MgO(s) + CO2(g) H o = +117 kJ mol1 S o = +175 J K1 mol1 (i) Calculate the value of G o at 298 K for the above reaction. (ii) Use your answer to (i) to explain whether or not this reaction is spontaneous at 298 K.[1] [2]UCLES 2016 9701/42/F/M/16 [Total: 16] [Turn over<br />

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