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# Discussion5_ch17_072010_Answer - CHEM102 Discussion Class...

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CHEM102 Discussion Class 5 (Chapter 17) 1HCalculate the amount of useful energy that can be obtained for the following reaction and given data. Could this reaction be used as an energy source? 2 H 2 O(l) + H 2 S(aq) ––––> SO 2 (g) + 3 H 2 (g) ΔH f °(kJ/mol) ΔG f °(kJ/mol) H 2 (g) (you should know these values) H 2 O(l) -285.83 -237.13 SO 2 (aq) -296.83 -300.19 H 2 S(aq) -39.70 -27.83 Useful energy is HG°: ΔG° = [(1)(-300.19) + (3)(0.00)] – [(2)(-237.13) + (1)(-27.83)] = 201.90 kJ/mol Since ΔG° is large and positive, no useful energy can be obtained from this reaction. 2. What are signs forΔG 0 , ΔH 0 , ΔS 0 for the spontaneous condensation of a vapor to a liquid? ΔG 0 <0 ΔH 0 <0 ΔS 0 <0 3. a) CalculateΔS 0 sys for the following synthesis reaction at 298K, N2 (g) + 3H2(g) ––––>2 NH3 (g) ΔS 0 (J/molK) 191.6 130.7 192.5 ΔH 0 (KJ/mol)) -46.2 S 0 rxn = n p S 0 (products) - n r S 0 (reactants) -199 J/K b) Calculate ΔS 0 univ. At 298K S univ = S sys + S surr

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