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Unformatted text preview: To (st22362) Homework 3 Fakhreddine (52420) 1 This printout should have 29 questions. Multiplechoice questions may continue on the next column or page find all choices before answering. 001 1.0 points A: The standard reaction free energy at equi librium is zero. B: A reaction stops when the equilibrium is reached. C: An equilibrium reaction is not affected by increasing the concentrations of products. Which of these statements is/are true? 1. Only B is true. 2. Only A and B are true. 3. A, B, and C are true. 4. Only A is true. 5. Only C is true. 6. None is true. correct 7. Only B and C are true. 8. Only A and C are true. Explanation: A: false; The standard reaction free energy G r is not 0 at equilibrium. The reaction free energy G r , which is dependent upon the concentrations of the products and reactants, is 0 at equilibrium. B: false; Equilibrium is dynamic. At equi librium, the concentrations of reactants and products will not change, but the reaction will continue to proceed in both directions. C: false; Equilibrium reactions are affected by the presence of both products and reac tants. 002 1.0 points Write the equilibrium constant for 2 NaBr(aq) + Pb(ClO 4 ) 2 (aq) PbBr 2 (s) + 2 NaClO 4 (aq) . 1. K = [NaClO 4 ] 2 [NaBr] 2 [Pb(ClO 4 ) 2 ] 2. K = 1 [Pb 2+ ][Br ] 2 correct 3. K = [Pb 2+ ][Br ] 2 4. K = [PbBr 2 ] [Pb 2+ ][Br ] 2 5. K = 1 [Pb(ClO 4 ) 2 ][NaBr] 2 Explanation: 003 1.0 points Consider the famous ammonia preparation 3 H 2 (g) + N 2 (g) 2 NH 3 (g) The equation K = [ x ] 2 [0 . 1 3 x ] 3 [0 . 7 x ] is not a possible correct description of the equilibrium situation because 1. [ x ] in the numerator should be [2 x ]. cor rect 2. [0 . 7 x ] in the denominator should be [0 . 7 3 x ]. 3. The equation is correct. 4. the denominator and numerator should be inverted. 5. the 0.1 and 0.7 in the denominator are incompatible. Explanation: 3 H 2 (g) + N 2 (g) 2 NH 3 (g) ini, M 0.1 0.7 , M 3 x x +2 x eq, M . 1 3 x . 7 x 2 x K = [NH 3 ] 2 [H 2 ] 3 [N 2 ] = (2 x ) 2 (0 . 1 3 x ) 3 (0 . 7 x ) To (st22362) Homework 3 Fakhreddine (52420) 2 004 1.0 points Knowing only the H rxn and S of each of the different reactions I) H rxn = 10 J/mol, S = 1000 J/K/mol II) H rxn = 10 J/mol, S = 1000 J/K/mol III) H rxn = 20 J/mol, S = 1000 J/K/mol IV) H rxn = 40 J/mol, S = 2000 J/K/mol which will have the highest K eq value? As sume all reactions are run at 293 K. 1. IV only 2. III only correct 3. All four have equal values of K . 4. I only 5. I, II and III have equal highest values of K . 6. II only 7. I and II have equal highest values of K . Explanation: 005 1.0 points The standard molar Gibbs free energy of for mation of NO 2 (g) at 298 K is 51.30 kJ mol 1 and that of N 2 O 4 (g) is 97.82 kJ mol 1 ....
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 Spring '10
 McCord
 Chemistry

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