OCR A Jun 2014 Paper 2 Q4

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This question is about the determination of enthalpy changes. 10 (a) A student carries out an experiment to find the enthalpy change of reaction, Hr, for the reaction below. Na2CO3(s) + 2HCl(aq) 2NaCl(aq) + CO2(g) + H2O(l) In the experiment, 3.18 g of Na2CO3 are added to 50.0 g of 2.00 mol dm3 HCl, an excess. The temperature of the reaction mixture increases by 5.5 C. Calculate Hr, in kJ mol1. Give your answer to three significant figures. The specific heat capacity, c, of the reaction mixture is 4.18 J g1 K1. Hr =kJ mol1 [4]OCR 2014<br />
 11 (b) The booster rocket of a spacecraft uses a mixture of aluminium and ammonium chlorate(VII), NH4ClO4, as a fuel. The equation and some enthalpy changes are shown below. 3Al(s) + 3NH4ClO4(s) Al2O3(s) + AlCl3(s) + 6H2O(g) + 3NO(g) H = 2677 kJ mol1 Substance NH4ClO4(s) Al2O3(s) AlCl3(s) H2O(g) Standard enthalpy change of formation, Hf / kJ mol1 295 1676 704 242 (i) What is meant by the term standard enthalpy change of formation? Give the standard conditions.[3] (ii) Write the equation, including state symbols, for the reaction that represents the standard enthalpy change of formation of NH4ClO4(s).[2] (iii) Calculate the enthalpy change of formation of NO(g) using the data above. enthalpy change of formation of NO(g) =kJ mol1 [3] [Total: 12]OCR 2014 Turn over<br />

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