CIE Nov 2016 v2 Paper 4 Q3

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PMT Iron has atomic number 26. (a) Complete the electronic con guration for the iron atom and the iron ion in the +3 oxidation state. iron atom [Ar]iron ion in the +3 oxidation state [Ar][2] (b) Fe3+ can act as a homogeneous catalyst in the reaction between peroxodisulfate ions (S2O8 and iodide ions. 2) (i) What is meant by a homogeneous catalyst?[1] (ii) Write an equation for the overall reaction between S2O8 2(aq) and I(aq).[1] (iii) Suggest why, in the absence of a catalyst, the activation energy for this reaction is high.[1] (iv) Write two equations to show how Fe3+(aq) ions can catalyse the reaction between S2O8 2(aq) ions and I(aq) ions. equation 1equation 2[2]UCLES 2016 9701/42/O/N/16<br /> PMT (c) Iron(III) oxide can be reduced to iron metal using carbon monoxide at a temperature of 1000 C. Fe2O3(s) + 3CO(g)2Fe(s) + 3CO2(g) H o =43.6 kJ mol1 Some relevant standard entropies are given in the table. substance Fe2O3(s) S o / J K1 mol1 +90 CO(g) +198 Fe(s) +27 CO2(g) +214 (i) What is meant by the term entropy ?[1] (ii) Calculate the standard entropy change, S o, for this reaction. (iii) Calculate the standard Gibbs free energy change, G o, for this reaction at 25 C. S o =J K1 mol1 [2] G o =kJ mol1 [2] (iv) Suggest why a temperature of 1000 C is usually used for this reaction, even though the reaction is spontaneous (feasible) at 25 C. Explain your answer.[1] [Total: 13]UCLES 2016 9701/42/O/N/16 [Turn over<br />

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