CHM152 Name:KEY Fall 2013 Exam 3 – Chapters 18 & 19 1.(3 pts) Which statement is correct? a.Heating always decreases the entropy of a system. b.The reaction that results in an increase in the number of moles of gas always decreases the entropy of a system. c.The greater number of particles leads to a smaller number of microstates. d.An increase in the temperature decreases all types of molecular motions. e.The dissolving process usually leads to an increase in entropy. 2.(3 pts) Which of these species has the highest entropy at 25oC? 3.(6 pts) Calculate ΔS° at 25°C for the reduction of PbO(s) from 2 PbO (s) + C(s) →2 Pb (s) + CO2 (g)given these absolute entropies: S° (J/K • mol) Answer = 198.8 J/K PbO (s) 69.45 C (s) 5.7 Pb (s) 64.89 CO2(g) 213.6 4.(6 pts) Ozone (O3) in the atmosphere can reaction with nitric oxide (NO): O3 (g) + NO (g) →NO2 (g) + O2 (g). Calculate the ΔG° for this reaction at 25°C. (ΔH° = –199 kJ/mol, ΔS° = –4.1 J/K • mol) ΔG° = -2.0 x 102kJ 5.(3 pts) For a chemical reaction to be spontaneous only at high temperatures, which of the following conditions must be met?
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