CIE Nov 2016 v3 Paper 4 Q3

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The spontaneity (feasibility) of a chemical reaction depends on the standard Gibbs free energy change, G o. This is related to the standard enthalpy and entropy changes by the equation shown. PMT G o = H oTS o (a) State and explain whether the following processes will lead to an increase or decrease in entropy. (i) the reaction of magnesium with hydrochloric acid entropy changeexplanation[1] solid potassium chloride dissolving in water entropy changeexplanation[1] steam condensing to water (ii) (iii) entropy changeexplanation[1] (b) Magnesium carbonate can be decomposed. MgCO3(s)MgO(s) + CO2(g) H o = +117 kJ mol1 Standard entropies are shown in the table. substance MgCO3(s) S o / J mol1 K1 +65.7 MgO(s) +26.9 CO2(g) +214 (i) Calculate G o for this reaction at 298 K. Include a relevant sign and give your answer to three significant figures. G o =kJ mol1 [3] (ii) Explain, with reference to G o, why this reaction becomes more feasible at higher temperatures.[1]UCLES 2016 9701/43/O/N/16<br /> (c) On heating, sodium hydrogencarbonate decomposes into sodium carbonate as shown. PMT 2NaHCO3(s)Na2CO3(s) + CO2(g) + H2O(g) H o = +130 kJ mol1 S o = +316 J mol1 K1 Calculate the minimum temperature at which this reaction becomes spontaneous (feasible). Show your working. temperature =K [2] (d) The solubility of Group 2 sulfates decreases down the Group. Explain this trend.[2] [Total: 11]UCLES 2016 9701/43/O/N/16 [Turn over<br />

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