Spring '11 Exam 3 with Answers

Which of the following statements best explains why

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15. Which of the following statements best explains why entropy increases with temperature? A. As temperature increases, the number of molecules increases. B. As temperature increases, energy levels become more closely spaced. C. As temperature increases, the molecules become more energetic and can access more energy levels. D. As temperature increases, the molecules dissociate into atoms, and the more atoms, the higher the entropy. E. As temperature increases, the number of bonds in molecules increases.
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6 16. Which of the following reactions is/are expected to have positive Δ G o rxn value(s) at 25°C? (i) AgBr(s) Ag + (aq) + Br - (aq) K sp = 7.7 × 10 - 13 (ii) HNO 2 (aq) + H 2 O( l ) NO 2 - (aq) + H 3 O + (aq) K a = 4.5 × 10 - 4 (iii) N 2 (g) + O 2 (g) 2 NO(g) K p = 4.0 × 10 - 31 A. none B. (iii) only C. (i) and (ii) only D. (i) and (iii) only E. all 17. Consider the following reaction: H 2 O( l ) H + (aq) + OH - (aq) K w = 1.0 × 10 - 14 at 25 °C What is the value of Δ G rxn at 25 °C when [H + ] = 1.0 × 10 - 7 M and [OH - ] = 1.0 × 10 - 7 M ? 18. The melting point of sodium is 98 °C. At the melting point, solid and liquid sodium are at equilibrium with each other. Which of the following is/are correct for sodium at 98 °C? (i) Δ S universe = 0 (ii) Δ S surr = - Δ S sys (iii) Δ S surr < Δ S sys (iv) Δ G sys = 0
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7 19. The dissolution of ammonium nitrate, NH 4 NO 3 , in water to form an aqueous solution is spontaneous, even though it is endothermic. Which of the following statements is correct ? 20. Δ G o for the reaction: H 2 (g) + I 2 (g) 2 HI(g) is 2.60 kJ/mol at 25 °C. Calculate Δ G and predict the direction in which this reaction is spontaneous if the starting concentrations are P(H 2 ) = 3.5 atm, P(I 2 ) = 1.5 atm, and P(HI) = 1.75 atm. Note: both parts of the answer must be correct for credit.
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