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Physical Chemistry for Engineers 1 Problem Set no. 3 Thermochemistry / Second Law of Thermodynamics For all items, observe 2 decimal places in the final answers. 1) Calculate the change in entropy when 25 kJ of energy is transferred reversibly and isothermally as heat to a large block of iron at (a) 0°C, (b) 100°C. 2) Calculate ΔS (for the system) when the state of 3.00 mol of perfect monoatomic gas atoms is changed from 25°C and 1.00 atm to 125°C and 5.00 atm. How do you rationalize the sign of ΔS? 3) A sample consisting of 3.00 mol of diatomic perfect gas molecules at 200 K is compressed reversibly and adiabatically until its temperature reaches 250 K. Given that CV,m = 27.5 J K−1 mol−1, calculate q, w, ΔU, ΔH, and ΔS.



4) Calculate ΔH and ΔStot when two copper blocks, each of mass 10.0 kg, one at 100°C and the other at 0°C, are placed in contact in an isolated container. The specific heat capacity of copper is 0.385 J K−1 g−1 and may be assumed constant over the temperature range involved. 5) The enthalpy of vaporization of chloroform (CHCl3) is 29.4 kJ mol−1 at its normal boiling point of 334.88 K. Calculate (a) the entropy of vaporization of chloroform at this temperature and (b) the entropy change of the surroundings. 6) Calculate the standard reaction entropy at 298 K of a) 2CH3CHO(g) + O2(g) à 2CH3COOH(l) b) 2 AgCl(s) + Br2(l) → 2 AgBr(s) + Cl2(g) c) Hg(l)+Cl2(g)→HgCl2(s) 7) The standard enthalpy of decomposition of the yellow complex H3NSO2 into NH3 and SO2 is +40 kJ mol−1. Calculate the standard enthalpy of formation of H3NSO2. 8) Given the reactions (1) and (2) below, determine (a) ΔrH0 and ΔrU0 for reaction (3), (b) ΔfH for both HCl(g) and H2O(g) all at 298 K. (1) H2(g) + Cl2(g) → 2 HCl(g) ∆rH0 = −184.62 kJ mol−1 (2) 2 H2(g) + O2(g) → 2 H2O(g) ∆rH0 = −483.64 kJ mol−1 (3) 4 HCl(g) + O2(g) → Cl2(g) + 2 H2O(g) 9) When 120 mg of naphthalene, C10H8(s), was burned in a bomb calorimeter the temperature rose by 3.05 K. Calculate the calorimeter constant. By how much will the temperature rise when 10 mg of phenol, C6H5OH(s), is burned in the calorimeter under the same conditions? 10) Calculate the standard enthalpy of solution of AgCl(s) in water from the enthalpies of formation of the solid and the aqueous ions.