Edexcel Jan 2017 (IAL) Paper 3 Q3

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3 A student carried out two similar, separate experiments to determine the enthalpy changes for the reactions of sodium hydrogencarbonate and sodium carbonate with excess dilute hydrochloric acid. (a) The first experiment was to find the enthalpy change H1 for the reaction NaHCO3(s) + HCl(aq)NaCl(aq) + H2O(l) + CO2(g) Results Measurement Mass of solid sodium hydrogencarbonate added to hydrochloric acid Volume of hydrochloric acid Initial temperature of hydrochloric acid before addition of solid sodium hydrogencarbonate Final temperature of solution Value 4.20 g 50.0 cm3 21.0 C 14.0 C Molar mass of sodium hydrogencarbonate 84.0 g mol1 Specific heat capacity of solution 4.18 J g1 C1 *P48371A0616*<br /> (i) Calculate the number of moles of sodium hydrogencarbonate used in the experiment. (1) moles of NaHCO3 =mol (ii) Calculate the heat energy absorbed in the reaction between sodium hydrogencarbonate and hydrochloric acid. Use the expression: Energy absorbed (J) = 50.0specific heat capacity of solutiontemperature change (1) energy absorbed =J (iii) Calculate the value of H1. Your answer should be in units of kJ mol1, expressed to three significant figures, and include a sign. (3) H1 =kJ mol1 *P48371A0716* Turn over<br /> (b) In the second experiment, the enthalpy change for the reaction between sodium carbonate and dilute hydrochloric acid was determined. Na2CO3(s) + 2HCl(aq)2NaCl(aq) + H2O(l) + CO2(g) The molar enthalpy change of this reaction H2 was found to be 36.0 kJ mol1. (i) Describe two ways in which the temperature change differs when equal numbers of moles of sodium hydrogencarbonate and sodium carbonate are reacted separately with the same volume of excess dilute hydrochloric acid. (2) First differenceSecond difference(ii) State one assumption that has been made when calculating the values of H1 and H2 from the experimental results. (1)*P48371A0816*<br /> (c) The results of the experiments in parts (a) and (b) may be used to calculate the enthalpy change of reaction for the thermal decomposition of sodium hydrogencarbonate. The equation for the reaction is 2NaHCO3(s)Na2CO3(s) + H2O(l) + CO2(g) Hreaction (i) Complete the Hess cycle. Include state symbols with any formulae. 2NaHCO3(s) Hreaction Na2CO3(s) + H2O(l) + CO2(g) +2HCl(aq) +2HCl(aq) (2) (1) (ii) Using the Hess cycle, or otherwise, complete the expression for Hreaction in terms of enthalpy changes H1 and H2. Hreaction = (iii) Use your value for H1 calculated in part (a)(iii), the value of H2 = 36.0 kJ mol1 and your expression in (c)(ii), to calculate a value for Hreaction in kJ mol1. (1) Hreaction =kJ mol1 (Total for Question 3 = 12 marks) *P48371A0916* Turn over<br />

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