Edexcel Jun 2015 Paper 1 Q20

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20 The reaction of calcium oxide with hydrochloric acid is an exothermic reaction. CaO(s) + 2HCl(aq)CaCl2(aq) + H2O(l) In an experiment to investigate this reaction, the following procedure was carried out. 1. 50.0 cm3 of hydrochloric acid, concentration 2.0 mol dm3 (an excess), was pipetted into a polystyrene cup and the initial temperature measured using a thermometer with 0.5C graduations. 2. 1.46 g of calcium oxide powder was weighed out and added to the acid. The mixture was stirred and the maximum temperature measured. Maximum temperature / C Initial temperature / C 35.0 19.5 (a) Calculate the enthalpy change, in joules, for the quantities in this experiment. Assume that the specific heat capacity of the solution is 4.18 J g1 C1. Use the expression: energy transferred in joules = 50.0specific heat capacitytemperature change (b) Using your answer from (a), calculate the molar enthalpy change for the reaction between calcium oxide and hydrochloric acid. Include a sign and units in your answer. (1) (2) 20 *P44879A02024*<br /> (c) The standard molar enthalpy change for the reaction between calcium oxide and hydrochloric acid is 196.8 kJ mol1. (i) Suggest three reasons why the calculated value in part (b) is different from this value. (3) Reason 1Reason 2Reason 3(ii) Using the standard enthalpy change of 196.8 kJ mol1, calculate the minimum mass of calcium oxide that would be needed to raise the temperature of 250 cm3 of hydrochloric acid (an excess) by 25.0C. (3) *P44879A02124* 21 Turn over<br /> (d) The reaction of calcium carbonate with hydrochloric acid has the following standard molar enthalpy change. (cid:507)H(cid:57) = 18.8 kJ mol1 This value can be used, with the enthalpy change for the reaction of calcium oxide with hydrochloric acid, to determine the enthalpy change for the thermal decomposition of calcium carbonate. This cannot be measured directly. (i) Complete the Hess energy cycle below by adding the missing arrow and entities. Use the cycle, and the standard enthalpy change for the reaction of calcium oxide and hydrochloric acid (196.8 kJ mol1), to determine the standard enthalpy change for the decomposition of calcium carbonate. (4) CaCO3(s) CaO(s) + CO2(g) 2HCl(aq)( ) +( ) +( ) Enthalpy change =kJ mol1 22 *P44879A02224*<br /> (ii) Complete and label the enthalpy level diagram below, for the series of reactions in (d)(i). Your diagram does not have to be to scale. (1) CaO(s) + CO2(g) Enthalpy / kJ mol1 CaCO3(s) Progress of reaction (Total for Question 20 = 14 marks) TOTAL FOR SECTION B = 60 MARKS TOTAL FOR PAPER = 80 MARKS *P44879A02324* 23<br />

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