NAME ______________________________________________ © Keeney-Kennicutt, 2010 D1 CHEMISTRY 102 FALL 2010 EXAM 2 FORM D SECTION 502 DR. KEENEY-KENNICUTT Directions: (1) Put your name on PART 1 and your name and signature on PART 2 of the exam where indicated. (2) Sign the Aggie Code on PART 2 of this exam. (3) Each multiple choice question is actually 2 questions on your scanning sheet. If you are sure of an answer, put the same answer down for both questions for 5 pts. If you cannot decide between two answers, put your best answer down for the first (odd) question and the other answer down for the second (even) question. If you get the first one correct you'll get 3 pts; if you get the second one correct you’ll get 2 pts. If there is an ambiguous multiple choice question, use the last page to explain your answer. (4) Do NOT write on the envelope. (5) When finished, put everything in the envelope and wait to be excused. At the table, take everything out of the envelope. You can pick up the multiple choice part with the answers outside my office after 3pm. (6) There are a total of 35 questions (19 actual questions). PART 1 1&2. Which is the correct Kc expression for the equilibrium: Ni(s) + 4CO(g) →← Ni(CO)4(g) ? (a) Kc = [Ni(CO)4][Ni][CO] (b) Kc = [Ni][CO]4[Ni(CO)4] (c) Kc = [Ni(CO)4][CO]4 (d) Kc = [Ni(CO)4]4[CO] (e) Kc = [Ni(CO)4][Ni][CO]4 3&4. The units of the specific rate constant for a reaction that is third order overall is __________. (a) s-1 (b) M-2⋅s-1 (c) M-1⋅s-1 (d) M-3⋅s-1 (e) M⋅s-1 5&6. The principal reason for the increase in reaction rate with increasing temperature is: (a) molecules increase in size at high temperatures. (b) the pressure exerted by reactant molecules increases with increasing temperature. (c) the activation energy increases with increasing temperature. (d) the fraction of high energy molecules increases with increasing temperature. (e) the activation energy decreases with increasing temperature. 7&8. Which statement or statements is/are TRUE about the purpose of a catalyst? (1) Catalysts increase the number of collisions between the reactants in the overall reaction. (2) A catalyst cannot appear as a reactant in a rate law expression. (3) A catalyst lowers the activation energy of both the forward and reverse reaction. (a) 1 & 2 (b) 2 & 3 (c) 1 & 3 (d) only 1 (e) only 3© Keeney-Kennicutt, 2010 D2 9&10. Determine the activation energy for the reverse reaction if the ΔH = ΔE for the reaction is –30 kJ and the activation energy for the forward reaction is 70 kJ. (It may be useful to draw the potential energy diagram.) (a) +100 kJ (b) –100 kJ (c) +40 kJ (d) –40 kJ (e) +30 kJ 11&12. The rate law for the chemical reaction, 2ClO2(aq) + 2OH−(aq) → ClO3− (aq) + ClO2−(aq) + H2O(l) has been determined experimentally to be: Rate = k[ClO2]2[OH−] The reaction order with respect to the hydroxide ions is: (a) 3 (b) 2 (c) 1 (d) k[OH−]2 (e) k[ClO2]2[OH−] 13&14. The dilution of concentrated sulfuric acid can be dangerous because the temperature of the solution can increase so rapidly that the solution can boil. What are the signs of ∆H, ∆S and ∆G for this process? (a) ∆H<0, ∆S<0 and ∆G<0 (b) ∆H<0, ∆S>0 and ∆G<0 (c) ∆H<0, ∆S>0 and ∆G>0 (d) ∆H>0, ∆S>0 and ∆G<0 (e) ∆H>0, ∆S<0 and ∆G>0 15&16. Consider the equilibrium, B2 →← 2B with Kc >> 1. Which picture represents this system? (a) (b) (c) (d) (e)© Keeney-Kennicutt, 2010 D3 17&18. Consider the reaction: X + Y Æ Z. When the concentration of X is halved and the concentration of Y is tripled, the rate increases by a factor of 9/4. The appropriate rate law expression is: (a) Rate = k[X]2 (b) Rate = k[X]2[Y]2 (c) Rate = k[X]2[Y]3 (d) Rate = k[X]2[Y] (e) Rate = k[X][Y] 19&20. At what temperatures will a reaction be spontaneous if ΔH° = –12.7 kJ/mol rxn and ΔS° = –135 J/mol rxn·K. (a) The reaction will be spontaneous at any temperature. (b) The reaction will never be spontaneous. (c) All temperatures below 94.1 K (d) All temperatures above 94.1 K (e) Temperatures between 12.7 K and 135 K© Keeney-Kennicutt, 2010 D4 21&22. Rate data were collected for the following reaction at a particular temperature. What is the correct rate law expression? 2A + B + 3C → products Experiment [A]initial [B]initial [C]initial Initial Rate of Reaction 1 0.10 M 0.30 M 0.20 M 6.4 x 10-3 M/s 2 0.30 M 0.30 M 0.20 M 5.76 x 10-2 M/s 3 0.10 M 0.60 M 0.40 M 1.28 x 10-2 M/s 4 0.60 M 0.90 M 0.20 M 2.3 x 10-1 M/s 5 0.10 M 0.80 M 0.40 M 1.28 x 10-2 M/s (a) Rate = k[A][B][C] (b) Rate = k[B]2[C] (c) Rate = k[A][C]2 (d) Rate = k[A]2[C] (e) Rate = k[A]2 23&24. Consider the gas-phase equilibrium at a certain temperature: 2X →← Y A reaction begins with 2.0 moles of Y in a 1.0 L container. When the system reaches equilibrium, there is 1.0 mole of Y present. What is the value of the equilibrium constant, Kc? (a) 1 (b) 2 (c) 4 (d) 1/2 (e) 1/4© Keeney-Kennicutt, 2010 D5 25&26. Consider the following equilibrium in which the Kc = 36: 2 HBr(g) →← H2(g) + Br2(g) Initially in the container there is 0.30 M of HBr. At equilibrium, what is the concentration of HBr? (a) 0.15 M (b) 0.089 M (c) 0.018 M (d) 0.023 M (e) 0.14 M 27&28. Calculate the ∆G for the reaction at 25oC: N2O4(g) Æ N2(g) + 2 O2(g) Species ΔHo f 298 (kJ/mol) So (J/mol⋅K) N2O4(g) 9.16 304.2 N2(g) 0 191.5 O2(g) 0 205.1 (a) +827 kJ (b) –77.5 kJ (c) +691 kJ (d) –114 kJ (e) –97.8 kJ© Keeney-Kennicutt, 2010 D6 29&30. The activation energy for a reaction was determined to be 215 kJ/mol rxn. If the rate constant is 1.0 x 10–2 min–1 at 0oC, what would the rate constant be at when the temperature was raised to 25oC? ln⎝⎛⎠⎞k2k1 = – EaR ⎝⎛⎠⎞1T2 - 1T1 or ln⎝⎛⎠⎞k2k1 = EaR ⎝⎛⎠⎞T2 - T1T1T2 or ln⎝⎛⎠⎞k2k1 = EaR ⎝⎛⎠⎞1T1 - 1T2 R = 8.314 J/mol·K (a) 28 min–1 (b) 0.032 min–1 (c) 71 min–1 (d) 0.25 min–1 (e) 1.01 min–1 31&32. The decomposition of formic acid follows first-order kinetics: HCOOH(g) → CO2(g) + H2(g) At 550oC, the half-life for the reaction is 24.0