Chemistry Chapter 13 Rates of Reaction Part 2

Constants: R=8.314 x 10-3 kJ/mol-K 1. Which of the following expressions does NOT represent a proper expression for the rate of this reaction? 2A + 3B ---> F + 2G a) (-Δ[A])/(Δt) b) (Δ[F])/(Δt) c) (-Δ[B])/(3Δt) d) (Δ[G])/(2Δt) 2. Which of the following statements regarding collision and transition state theory is FALSE? a) Activation energy is always positive. b) Reactants must collide to form products. c) Reactant collisions must be oriented properly to form products. d) All reactant collisions result in product formation. e) Reactant molecules must absorb energy to form the transition state. 3. The gas phase reaction A + B ---> C has a reaction rate which is experimentally observed to follow the relationship rate = k[A]2[B]. If the concentration of A is tripled and the concentration of B is doubled, the reaction rate would be increased by a factor of __________. a) 12 b) 6 c) 36 d) 9 e) 18 4. The rate constant for the first order reaction A ---> B + C is k = 3.3 x 102 min-1 at 57 K. What is the half-life for this reaction at 57 K? a) 61 min b) 9.1 min c) 21 min d) 1200 min e) 30 min 5. Which of the following statements about catalysts are FALSE? a) In homogeneous catalysis the catalyst is in the same phase as the reactants. b) Catalyst are often transition metals and transition metal oxides. c) A catalyst can make a nonspontaneous reaction spontaneous. d) A catalyst speeds up both the forward and reverse reaction. e) A catalyst lowers the activation energy. 6. For the gas phase decomposition of dinitrogen pentoxide at 335 K the average rate of disappearance of N2O5 over the time period from t = 0 s to t = 154 s is found to be 6.0 x 10-4 M s-1. 2 N2O5 ---> 4 NO2 + O2 The average rate of formation of NO2 over the same time period is how many moles per liter per second? a) 6.0 x 10-4 M s-1 b) 1.2 x 10-3 M s-1 c) 3.0 x 10-4 M s-1 d) 2.4 x 10-3 M s-1 7 .The oxidation of arsenate ion by cerium(IV) ion in aqueous solution: AsO33- + 2 Ce4+ + H2O ---> AsO43- + 2 Ce3+ + 2 H+ is first order in AsO33- and second order in Ce4+. In an experiment to determine the rate law, the rate constant was determined to be 0.70 M-2s-1. Using this value for the rate constant, the rate of the reaction when [AsO33-] = 3.2 x 10-2 M and [Ce-4+] = 0.60 M would be how many mole per liter per second? a) 1.3 x 10-2 M s-1 b) 8.1 x 10-3 Ms-1 c) 1.9 x 10-2 M s-1 d) 1.5 x 10-2 M s-1 8. The following initial rate data are for the oxidation of arsenate ion by cerium(IV) ion in aqueous solution: AsO33- + 2 Ce4+ + H2O ---> AsO43-+ 2 Ce3+ + 2 H+ Experiment [AsO33-]o, M [Ce4+]o, M Initial Rate, Ms-1 ---------------------------------------------------------------------------------------------------------------------------1 3.66 x 10-2 0.446 4.07 x 10-3 -2 2 7.32 x 10 0.446 8.14 x 10-3 3 3.66 x 10-2 0.893 1.63 x 10-2 4 7.32 x 10-2 0.893 3.26 x 10-2 Give the rate law for this reaction by supplying the exponent of the arsenate ion concentration, followed by the exponent of the cerium ion concentration. a) 2,1 b) 1,1 c) 2,2 d) 1,2 e) 1,4 9. In a study of the gas phase decomposition of sulfuryl chloride SO2Cl2 ---> SO2 + Cl2 at 600 K the concentration of SO2Cl2 was followed as a function of time. It was found that a graph of ln[SO2Cl2] versus time in minutes gave a straight line with a slope of -3.9 x 10-3 min-1 and a y-intercept of -5.9. Based on this plot, the reaction is what order in SO2Cl2 and the rate constant for the reaction is what value? a) 1st order, k = 5.9 min-1 b) 2nd order, k = 3.9 x 10-3 min-1 c) 1st order, k = 3.9 x 10-3 min-1 d) 2nd order, k = 5.9 min-1 e) 1st order, k = 6.6 x 10-4 min-1 10. Decomposition of nitramide NH2NO2(aq) ---> N2O(g) + H2O(l) in aqueous solution at 25°C is first order in NH2NO2 with a rate constant of 4.70 x 10-5 s-1. If the initial concentration of NH2NO2 is 0.322 M, how much time must elapse in seconds so that the concentration of NH2NO2 will be 7.21 x 10-2 M? a) 6.85 x 103 s b) 8.08 x 104 s c) 2.12 x 104 s d) 4.70 x 10-5 s e) 3.18 x 104 s 11. The gas phase decomposition of nitrosyl chloride 2 NOCl ---> 2 NO + Cl2 at 400 K is second order in NOCl. In one experiment, when the initial concentration of NOCl was 3.78 x 10-2 M, the concentration of NOCl dropped to 3.82 x 10-3 M after 3.07 x 105 seconds had passed. Based on these data, the rate constant for the reaction is what value ? a) 4.97 x 10-3 M-1s-1 b) 7.97 x 10-6 M-1s-1 c) 7.67 x 10-4 M-1s-1 d) 3.25 x 10-6 M-1s-1 12. The following data are for the gas phase decomposition of phosphine 4 PH3(g) ---> P4(g) + 6 H2(g) at 120°C. Based on these data, the rate constant for this 1st order reaction equals what per second? (Hint: unnecessary to graph this data.) [PH3], 4.64 x 10-2 2.32 x 10-2 1.16 x 10-2 5.80 x 10-3 Molar concentration -------------------------------------------------------------------------------------------------------------------------------------------------seconds 0 28 56 84 a) 2.47x10-2 s-1 b) 28 s-1 c) 4.64 x 10-2 s-1 d) 3.57 x 10-2 s-1 13. A reaction profile (not to scale!) for the reaction is shown below: C2H5Cl ---> C2H4 + HCl What is the activation energy of the REVERSE reaction, and is the FORWARD reaction exothermic or endothermic? a) 70 kJ and endothermic forward reaction b) 205 kJ and exothermic forward reaction c) 275 kJ and endothermic forward reaction d) 275 kJ and exothermic forward reaction e) 205 kJ and endothermic forward reaction Problems #14-16: A proposed mechanism for one of the pathways for the destruction of ozone in the atmosphere is: slow: O3 + NO ---> NO2 + O2 fast: NO2 + O ---> NO + O2 14. Which species acts as a catalyst? a) O3 b) NO c) NO2 d) O e) none 15. Which species are intermediates: a) O b) NO c) O2 d) NO2 e) none 16. Which rate law for the overall reaction is consistent with this mechanism. a) k [O3][NO] b) k [NO2][O] c) k [O][O3][NO] d) k [O3][NO][O] e) k [O3][NO][NO2] 17. The following mechanism has been proposed for the gas phase reaction of nitrogen monoxide with bromine: step 1 step 2 .fast: slow: NO + Br2 <---> NOBr2 NOBr2 + NO ---> 2 NOBr What is the rate law for the overall reaction that is consistent with this mechanism? a) k [NOBr2][NO] b) k [NO][Br2] c) k [NO]2[Br2] d) k [NO][Br]2 e) k [NOBr2][NO][Br2] 18. For the gas phase isomerization of methyl cis-cinnamate cisC6H5CH=CHCOOCH3 ---> trans-C6H5CH=CHCOOCH3 the rate constant has been determined at several temperatures. When ln k in s-1 is plotted against the reciprocal of the Kelvin temperature, the resulting linear plot has a slope of -2.09 x 104 K and a y-intercept of 24.3. What is the activation energy this reaction in kJ? a) 24.3 kJ b) 2.09 x 104 kJ c) 174 kJ d) -2.09 x 104 kJ e) 48.6 kJ 19. Consider a chemical reaction involving compounds A and B, which is found to be first order in A and second order in B. At what rate will the reaction occur in experiment 2? Experiment Rate (M s-1) Initial [A] Initial [B] ---------------------------------------------------------------------------------------------------------------------------------------------1 0.10 1.0 M 0.20 M 2 ? 2.0 M 0.60 M a) 1.8 M s-1 b) 0.20 M s-1 c) 1.2 M s-1 d) 0.36 M s-1 e) 0.60 M s-1 20. A first-order reaction has a rate constant of 0.00300 s-1. The time required for 85% reaction is: a) 23.5 s b) 54.2 s c) 632 s d) 316 s e) 275 s 21. An elementary process has an activation energy of 40 kJ/mol. If the enthalpy change for the reaction is 30 kJ/mol, what is the activation energy for the reverse reaction? a) 50 kJ/mol b) 40 kJ/mol c) -40 kJ/mol d) 30 kJ/mol e) 10 kJ/mol 22. If the rate of a reaction increases by a factor of 64 when the concentration of reactant increases by a factor of 4, the order of the reaction with respect to this reactant is: a) 3 b) 16 c) 4 d) 1 e) 2 23. NO reacts with chlorine in a gas phase reaction to form nitrosyl chloride, NOCl. From the following experimental data, determine the form of the equation that describes the relationship of reaction rate to initial concentrations of reactants. 2 NO + Cl2---> 2 NOCl Run Initial [NO] Initial [Cl2] Initial Rate of Formation of NOCl -----------------------------------------------------------------------------------------------------------------------------------------------------1 0.50 M 1.00 M 1.14 M/hr 2 1.00 M 1.00 M 9.12 M/hr 3 1.00 M 0.50 M 4.56 M/hr a) rate = k[NO]2[Cl2] b) rate = k[NO][Cl2] c) rate = k[NO] d) rate = k[NO]2 e) rate = k[NO]2[Cl2]2 24. Consider the mechanism: O3(g) <---> O2(g) + O(g); fast O(g) + O3(g) ---> 2 O2(g); slow An intermediate in this reaction is: a) O3(g) b) There is no intermediate in this reaction c) O(g) d) O2(g) and O(g) e) O2(g) 25. The units of the rate constant for a second order reaction could be __________. a) M s-1 b) M2 s-1 c) s-1 d) M-1 s-1 e) M 26. When a catalyst is used in a reaction, a) the forward reaction is increased while the reverse reaction is retarded. b) it does not affect the final amounts of reactants and products. c) the enthalpy change for the reaction becomes more exothermic. d) the activation energy of the reverse reaction is increased. e) the activation energy for the forward reaction is not changed. 27. Given the following data for the NH4+ + NO2- ---> N2 + 2H2O reaction: Trial [NH4+] [NO2-] Rate --------------------------------------------------------------------------------------------------------------------------------1 0.010 M 0.020 M 0.020 M/s 2 0.015 0.020 0.030 3 0.010 0.010 0.005 The rate law for the reaction is: a) rate = k[NH4+][NO2-] b) rate = k[NH4+][NO2-]2 c) rate = k[NH4+]2[NO2-] d) rate = k[NH4+]2 [NO2-]2 e) None of the above 28. The reaction 2 NO2(g) ---> 2NO(g) + O2(g) is postulated to occur via the mechanism below: NO2(g) + NO2(g) ---> NO(g) + NO3(g); k1, slow NO3(g) ---> NO(g) + O2(g); k2, fast The rate law for this mechanism is: a) rate = k1k2[NO3]2 b) rate = k2[NO3] c) rate = k1[NO2]2 d) rate = k1 k2[NO2]2[NO3] e) rate = k1[NO2] 29. Reaction rates increase with increasing temperature because __________. a) the activation energy is decreased. b) the energy of the transition state is lowered. c) the activation energy increases. d) larger molecules collide more frequently. e) a greater fraction of molecules possess the activation energy when they collide. 30. Consider the following reaction: 2 N2O(g) ---> 2 NO(g) + O2(g); rate = k[N2O] If the half-life for the reaction is 0.910 s, the rate constant is: a) 1.1 s-1 b) 0.69 s-1 c) 1.3 s-1 d) 0.32 s-1 e) 0.76 s-1 KEY 1)a 2)d 3)e 4)c 5)c 6)b 7)b 8)d 9)c 10)e 11)c 12)a 13)e 14)b 15)d 16)a 17)c 18)c 19)a 20)c 21)e 22)a 23)a 24)c 25)d 26)b 27)b 28)c 29)e 30)e