Edexcel Jun 2017 (IAL) Paper 1 Q22

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22 Sodium hydrogencarbonate decomposes on heating to form sodium carbonate, carbon dioxide and water. Reaction 1 2NaHCO3(s) (cid:111) Na2CO3(s) + H2O(l) + CO2(g) (a) Suggest why it is difficult to measure the enthalpy change of this reaction directly. (1)D O N O T W R I T E I N T H I S A R E A (b) The enthalpy change can be measured indirectly using the enthalpy changes for the following two reactions and applying Hesss Law. Reaction 2 NaHCO3(s) + HCl(aq) (cid:111) NaCl(aq) + H2O(l) + CO2(g) Reaction 3 Na2CO3(s) + 2HCl(aq) (cid:111) 2NaCl(aq) + H2O(l) + CO2(g). An experiment was carried out to measure the enthalpy change of Reaction 2. 100 cm3 of 1.25 mol dm3 hydrochloric acid was placed in a polystyrene beaker with capacity 200 cm3. The initial temperature of the acid was 21.5(cid:113)C. 8.00 g of solid sodium hydrogencarbonate was added, a lid was placed on the beaker and the mixture was stirred. The lowest temperature of the mixture was 14.2(cid:113)C. (i) Explain why the beaker used in this experiment is large. (1) D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A(ii) Show by calculation that the hydrochloric acid is present in excess. (2) 18 *P48382A01824*<br /> (iii) Calculate the energy transferred and hence the enthalpy change of the reaction in kJ mol1. Include a sign and units in your answer. Use the equation: Energy transferred (J) = 1004.18temperature change. (iv) The enthalpy change for Reaction 3 was found to be 36.3 kJ mol1. Complete the Hess cycle by adding the appropriate arrows and formulae to the outline. Use your completed cycle to calculate the enthalpy change for Reaction 1. 2NaHCO3(s) Reaction 1 Na2CO3(s) + H2O(l) + CO2(g) (3) (4) (cid:507)H for Reaction 1 =kJ mol1 (Total for Question 22 = 11 marks) A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D *P48382A01924* 19 Turn over<br />

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