Edexcel Jan 2016 (IAL) Paper 3 Q4

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4 The thermal decomposition of copper(II) carbonate is CuCO3(s) (cid:111) CuO(s) + CO2(g) Equation 3 The enthalpy change for this reaction, (cid:168)H3, cannot be determined directly. However, it can be calculated using Hesss law, from the enthalpy changes for the reaction of sulfuric acid with copper(II) carbonate and with copper(II) oxide. (a) A student carried out an experiment to determine the enthalpy change, (cid:168)H4, for the reaction CuCO3(s) + H2SO4(aq) (cid:111) CuSO4(aq) + H2O(l) + CO2(g) Equation 4 In the experiment, a known mass of copper(II) carbonate was mixed with a known volume of sulfuric acid in a polystyrene cup, and the temperature change measured. The results of the experiment are shown in the table. Measurement Mass of copper(II) carbonate added to sulfuric acid Volume of sulfuric acid, 1 mol dm3 Initial temperature of sulfuric acid before addition of copper(II) carbonate Maximum temperature of sulfuric acid after the addition of copper(II) carbonate Reading 2.54 g 50.0 cm3 24.3C 29.0C (i) Calculate the energy transferred, in joules, for this reaction using the expression Energy transferred (J) = 50.04.18temperature change (ii) Calculate the number of moles of copper(II) carbonate used. Molar mass of copper(II) carbonate = 123.5 g mol1 (1) (1) *P46939A01220* 12 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 D O N O T W R I T E I N T H I S A R E A<br /> A E R A S I H T N I E T I R W T O N O D (iii) Use your answers to (a)(i) and (a)(ii) to calculate, in kJ mol1, the enthalpy change, (cid:168)H4, for the reaction shown in Equation 4. Include a sign for (cid:168)H4 and give your answer to three significant figures. (iv) Why does the sulfuric acid need to be in excess? (2) (1)A E R A S I H T N I E T I R W T O N O D(v) The enthalpy change obtained from this experiment is much less negative than the Data Booklet value. Suggest one likely reason for this difference, other than a measurement error. (1)A E R A S I H T N I E T I R W T O N O D *P46939A01320* 13 Turn over<br /> (b) The student then carried out a similar experiment to determine the enthalpy change, (cid:168)H5, for the reaction between copper(II) oxide and sulfuric acid. CuO(s) + H2SO4(aq) (cid:111) CuSO4(aq) + H2O(l) Equation 5 From the results of this experiment, (cid:168)H5 was calculated to be 56.1 kJ mol1. The values of (cid:168)H4 and (cid:168)H5 can be used to determine the enthalpy change for the thermal decomposition of copper(II) carbonate using the Hess cycle shown below. CuCO3(s) (cid:168)H3 CuO(s) + CO2(g) + H2SO4(aq) (cid:168)H4 (cid:168)H5 + H2SO4(aq) CuSO4(aq) + CO2(g) + H2O(l) Use Hesss law to calculate the value of (cid:168)H3, in kJ mol1. Include a sign in your answer. (2) (c) Suggest why it is not possible to determine directly the enthalpy change for the thermal decomposition of copper(II) carbonate. (1)(Total for Question 4 = 9 marks) 14 *P46939A01420* 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 D O N O T W R I T E I N T H I S A R E A<br />

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