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Studocu is not sponsored or endorsed by any college or university Tutorial 5 Thermo Chemistry 1A (The University of Edinburgh) Studocu is not sponsored or endorsed by any college or university Tutorial 5 Thermo Chemistry 1A (The University of Edinburgh) Downloaded by Timothy Handoko (hantimo210@gmail.com) lOMoARcPSD|23633319

Tutorial Questions Chem1A Physical Chemistry (Thermodynamics) 1. When 0.113 g of benzene burns in an excess of O 2 in a constant pressure calorimeter with a measured heat capacity of 551 JK -1 the temperature rises from 21.3° C to 29.9° C. Calculate the enthalpy change, ∆ H, for the combustion of benzene. 2. A constant volume calorimeter showed that the heat loss accompanying the combustion of 1.000 mol of glucose was 2559 kJ at 298.15 K. Calculate the enthalpy of combustion, ∆ H, for glucose. 3. Find a source of the enthalpies of combustion for propane, carbon and hydrogen, and use these to calculate the standard enthalpy of formation of propane. 4. Use the standard enthalpies of formation given below to calculate the enthalpy of combustion of benzene. ∆ f H°298[C 6 H 6(l) ] = 49.0 kJmol -1 ∆ f H°298[CO 2(g) ] = -393.51 kJmol -1 ∆ f H°298[H 2 O (l) ] = -285.83 kJmol -1 5. Use the following information to construct a Born-Haber cycle to determine the lattice enthalpy of potassium chloride. ∆ f H°298[KCl (s) ] = -437 kJmol -1 ∆ H°[K (s) → K (g) ] = 89 kJmol -1 [enthalpy of vaporisation] ∆ H°[Cl 2 → Cl+Cl] = 244 kJmol -1 [bond dissociation enthalpy of Cl 2 ] IE = 418 kJmol -1 [1 st ionisation energy of K (g) ] EA = -394 kJmol -1 [electron affinity of Cl (g) ] Downloaded by Timothy Handoko (hantimo210@gmail.com) lOMoARcPSD|23633319

6. Find reference data for the enthalpy of combustion of octane and the enthalpies of formation of octane, water and carbon dioxide. Confirm that the enthalpy of the combustion reaction may be written as the sum of the enthalpies of formation of the products minus the sum of the enthalpies of reactants (Hess’s law). 7. Which substance in each pair below has the higher molar entropy? Give your reasoning. a) 1 mol of CO 2 in a 1dm 3 container or 1 mol of CO 2 in a 1m 3 container (same temperature) b) 1 mol of He at 25 ° C in a 20L container, or 1 mol of He at 100 ° C in a 20L container c) 1 mol Br 2(l) or 1 mol Br 2(g) (each at STP) d) 1 mol of CO at 0 K, or 1 mol of He at 0 K 8. Find reference data for the standard molar entropies of octane, oxygene, water and carbon dioxide. Calculate the standard molar entropy for the combustion of octane. From your answer to question 6 above, now calculate the standard molar Gibbs free energy change for the combustion reaction. 9. From the reference data for the standard free energy of formation of Al 2 O 3(s) at 25 ° C (and any additional necessary data you require), estimate the temperature at which the reduction of Al 2 O 3(s) with C (graphite) to form CO 2(g) and Al (s) becomes feasible. Briefly discuss potential shortcomings of your answer, i.e. why is it a crude estimate rather than an accurate value? Discussion points What have you learnt from thermodynamics that would help you to understand which fuel might be best for a particular task? Clue: what is the ∆ combustion H° for hydrogen, methane, octane, and methanol, and what is their respective enthalpy density? Downloaded by Timothy Handoko (hantimo210@gmail.com) lOMoARcPSD|23633319

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