OCR A Jan 2011 Paper 5 Q5

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5 Entropy changes are an important factor in determining the feasibility of reactions. 14 (a) You are provided with equations for four processes. A 2SO2(g) + O2(g) B H2O(l) H2O(g) C H2(g) + O2(g) D 2C(s) + O2(g) H2O(l) 2CO(g) 2SO3(g) For each process, explain why S has the sign shown below. A: sign of S: negative reason for sign:B: sign of S: positive reason for sign:C: sign of S: negative reason for sign:D: sign of S: positive reason for sign:[4]OCR 2011<br />
 (b) Calcium oxide, CaO, is used to make cement. Calcium oxide is manufactured by the thermal decomposition of calcium carbonate. 15 CaCO3(s) CaO(s) + CO2(g) H = +178 kJ mol1 Standard entropies of CaCO3(s), CaO(s) and CO2(g) are given in the table below. substance S / J K1mol1 CaCO3(s) 89 CaO(s) 40 CO2(g) 214Using the information in the table, show that the entropy change, S, for the decomposition of calcium carbonate is 0.165 kJ K1 mol1. Show that calcium carbonate is stable at room temperature (25 C).Calculate the minimum temperature needed to decompose calcium carbonate. Show all your working.OCR 2011 [7] [Total: 11] Turn over<br />

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