Spring 2011 Exam 1 for CHEM 188: Rate Laws and Equilibria - Prof. Peter Hierl, Exams of Chemistry

Download Spring 2011 Exam 1 for CHEM 188: Rate Laws and Equilibria - Prof. Peter Hierl and more Exams Chemistry in PDF only on Docsity! CHEM 188 – Spring, 2011 Hour Exam 1 (Red) February 17, 2011 Instructions: Your scantron answer sheet must show your NAME, 7-DIGIT KU ID NUMBER, and LAB SECTION. (Begin these entries at the LEFT end of the space provided.) In answering the questions, be careful to fill in the corresponding circles on the answer sheet according to the number of the question on the exam. USE A SOFT (No. 2) PENCIL.  Useful information: Gas constant, R = 8.314 J/K  mol = 0.08206 L  atm/K  mol Integrated Rate Laws: kt [A] 1 [A] 1 :orderSecond e[A] [A] :order-First kt - [A] [A] :order-Zero 0 kt 0 0     Arrhenius equation: /RT-Ea Ae k          21 21a 2 1 TT TT R E k k ln Relation of KP to KC: KP = KC(RT)n Quadratic formula: a acbb x 2 42   1 1. Consider the reaction 4PH3(g)  P4(g) + 6H2(g). Suppose that, at a particular moment during the reaction, H2(g) is being formed at the rate of 0.078 M/s. At what rate is P4(g) being formed? A. 0.013 M/s B. 0.052 M/s C. 0.078 M/s D. 0.117 M/s E. 0.47 M/s 2. For the overall chemical equation, 2H2S(g) + O2(g)  2S(s) + 2H2O(l) which one of the following can you rightly assume? 1. The rate law is, rate = k[H2S][O2] 2. The rate law is, rate = k[H2S]2[O2] 3. The reaction is second-order overall. 4. The reaction is third-order overall. 5. The rate law cannot be determined from the information given. A. 1 only B. 2 only C. 1 & 3 D. 2 & 4 E. 5 only 3. The rate law for the reaction shown below is given by rate = k[NH4+][NO2-]. NH4+(aq) + NO2-(aq) N2(g) + 2 H2O(l) At 25°C, the rate constant is 3.0 10-4/M s. Calculate the rate of the reaction at this temperature if [NH4+] = 0.050 M and [NO2-] = 0.080 M. A. 2.4  107 M/s B. 1.2  106 M/s C. 2.4  106 M/s D. 1.2  105 M/s E. none of the above 4. Consider the hypothetical reaction A + 2B  products. Use the following data to determine the rate law for the reaction. Expt. # [A]0 [B]0 Initial rate 1 0.20 0.20 1.46 M/min 2 0.30 0.20 3.29 M/min 3 0.30 0.50 8.21 M/min A. rate = k[A] B. rate = k[A][B] C. rate = k[A]2[B] D. rate = k[A][B]2 E. none of the above 2 17. The equilibrium constant, KC, for the reaction 2NO(g) + O2(g)  2NO2(g). is found to be 6.44 x 10 5 at 25oC. If the equilibrium concentrations of NO and O2 are 0.0600 M and 0.300 M, respectively, what is the equilibrium concentration of NO2? A. 0.0127 M B. 0.243 M C. 1.78 M D. 26.4 M E. 5.97 M 18. Consider the heterogeneous equilibrium process shown below. C(s) + CO2(g)  2 CO(g) At 700.°C, the total pressure of the system is found to be 1.50 atm. If the equilibrium constant KP is 1.52, calculate the equilibrium partial pressure of CO2. A. 0.31 atm B. 0.57 atm C. 0.57 atm D. 0.86 atm E. 0.93 atm 19. The equilibrium constant Kc for the decomposition of phosgene, COCl2, is 4.63 10-3 at 527°C. COCl2(g)  CO(g) + Cl2(g) If, in a reaction mixture at 527°C, the concentrations of COCl2, CO, and Cl2 are 0.25 M, 0.010 M, and 0.010 M, respectively, , then which one of the following statements is true? A. The system is at equilibrium; no change will occur. B. The concentrations of CO and Cl2 will fall as the system approaches equilibrium. C. The concentrations of CO and Cl2 will increase as the system approaches equilibrium. D. The concentration of COCl2 will rise as the system approaches equilibrium. E. None of the above 20. A sample consisting of 0.50 moles of AB(s) was placed in a 10.0 L reaction chamber at 750oC. After equilibrium was reached, it was found that 5.0% of the AB had dissociated according to the reaction 2AB(s)  2A(l) + B2(g) Calculate the equilibrium constant KC for this reaction at this temperature. A. 4.1 x 10 –7 B. 3.5 x 10 –6 C. 2.0 x 10 –5 D. 6.3 x 10 –4 E. 1.3 x 10 –3 21. Hydrogen and iodine react according to the equation H2(g) + I2(g)  2HI(g) Kc = 54.3 @ 1000 oC A mixture of 0.500 mol H2, 0.500 mol I2, and 0.100 mol of HI was placed in a 10.0 L reaction vessel at 1000oC. Calculate the concentration of H2 at equilibrium. A. 0.0117 M B. 0.0133 M C. 0.0160 M D. 0.0187 M E. 0.0213 M 5 22. At 250oC, the equilibrium constant Kp for the reaction below is 1.80. PCl5(g)  PCl3(g) + Cl2(g) If pure PCl5 is put into a reaction vessel at an initial pressure of 2.00 atm at 250oC, calculate the pressure of PCl5 after the system has reached equilibrium. A. 0.53 atm B. 0.80 atm C. 0.97 atm D. 1.20 atm E. 1.41 atm 23. For the dissociation reaction in aqueous solution AB2(aq)  A(aq) + 2B(aq) the equilibrium constant KC = 2.67 × 1010 at 25oC. If the initial concentration of AB2(aq) was 0.200 M, estimate the equilibrium concentration of B(aq). A. 2.37 × 104 M B. 3.77 × 104 M C. 4.74 × 104 M D. 5.98 × 104 M E. 7.53 × 104 M 24. For the dissociation of calcium carbonate to calcium oxide and carbon dioxide, CaCO3(s)  CaO(s) + CO2(g) the equilibrium constant on terms of concentration, KC, is 2.68 × 103 at 800oC. If 4.50 g of CaCO3 and 1.00 g of CaO were placed in an empty 10.0 L flask and the reaction allowed to come to equilibrium at 800oC, how many grams of CaCO3 would the flask contain? A. 0.320 g B. 0.820 g C. 1.32 g D 1.82 g E. 2.18 g 25. For the following reaction at equilibrium, which one of the changes below would cause the equilibrium to shift to the right? 2NOBr(g)  2NO(g) + Br2(g) Horxn = + 30 kJ 1. Increase the container volume. 2. Add some NO. 3. Remove some Br2. 4. Raise the temperature. 5. Decrease the temperature. A. 1 only B. 2 only C. 4 only D. 2 & 5 only E. 1, 3 & 4 6