Name: Date: CHE-112 —- CHAPTER 13 — PRACTICE QUESTIONS 1. Express the rate of the following reaction equation in terms of the rate of concentration change of NO2CI: 2 NO? (g) + Cl2 (g) ——+ 2 NO2Cl (g) A) rate of reaction = A[Cl2]/At B) rate of reaction =— 4 (A[NO2CI]/Ap) C) rate of reaction= 4 (A[NO2CI]/Ar) D) rate of reaction =— 4 (A[NO2]/Ad) 2. Express the rate of the following reaction equation in terms of the rate of concentration change of CHCl: CHC} (g) + Clo (g) ——+ CCl, (g) + HCl A) rate of reaction = A[CCl4]/At B) rate of reaction = 2(A[CHC13]/At) C) rate of reaction = A[CHCI3]/At D) rate of reaction = —A[CHCl3]/At 3. Let the rate of the reaction described by the equation H2 (g) + Bro (g) ——+ 2 HBr (g) be expressed as —A[Br2]/Az. Express the rate of reaction in terms of the rate of concentration change of HBr. A) rate of reaction =— % A[HBr]/At B) rate of reaction = —A[H2]/At C) rate of reaction = 4 A[HBr]/At D) rate of reaction = 2A[HBr]/At Page | 4. Let the rate of the reaction described by the equation Ho (g) + 2 ICI (g) —— 2 HCl (g) + h (g) be expressed as A[I2]/At. Express the rate of reaction in terms of the rate of concentration change of ICI. A) rate of reaction = A[ICI]/At B) rate of reaction =— % A[ICI]/At C) rate of reaction =—A[ICI]/At D) rate of reaction = —2A[ICI]/At 5. The rate law for the reaction described by the equation N20s (g) ——+ 2 NO» (g) + 4 O2 (g) at 343 K is first order in [N2O5] with a rate constant k = 1.80 h"!. Given that [N2Os]o = 0.112 M, calculate the rate of the reaction at t= 0. A) 0.112 Mh! B) 0.202 M.h! C) 1.80 M.h"! D) 69.1 M.h"! 6. The rate law for the reaction described by the equation NOz (g) —-+ NO(g) + % Oz (g) at 598 K is: rate of reaction = (0.54 M-!.s-!)[NO»]? Given that [NO2]o = 8.33 - 10-7 M, calculate the rate of the reaction at t= 0s. A) 3.7:107 Ms! B) 8.3-10°7 Ms! C) 3.7-103 Ms"! D) 6.9-:103 Ms! Page 2 7. The rate law for the reaction described by the equation CHC1 (g) + Cl2 (g) ——+ CCl (g) + HCl (g) is: rate of reaction = k[CHCI3][ Clo]! What is the overall order of this reaction? A) 1 B) 2 C) 3/2 D) 5/2 8. Nitrogen monoxide and oxygen react according to the reaction equation 2 NO (g) + O2 (g) ——+ 2 NO? (g) Using the following initial rate data, determine the rate constant for the reaction. Run [NO]o/M [O2]/M | Initial rate of formation of NO>(g)/MDs"! I 0.0228 0.0105 £35107 2 0.0456 0.0105 5.40: 10° 3 0.0228 0.0210 2.70: 10° A) 2.47 M?.s! B) 0.0564 M?.s"! C) 1.35- 1073 M?.s! D) 1.23 M?.s"! Page 3 2, 10. ih, I. Hydrogen peroxide decomposes according to the reaction equation 2 H2O2 (aq) ——+ 2 H20 (J) + Op (g) This reaction is first order in [H2O2] at 70°C with a rate constant of k = 0.0444 min“. If the initial concentration is [H202]o = 0.25 M, then what is the value of [H202] 45.0 minutes after the solution is prepared? A) 0.0043 M B) 0.035 M C) 0.055 M D) 0.15 M Argon-41 is a y-emitter with a half-life of 109.2 minutes. What fraction of a sample of Ar- 41 remains after 37.5 hours? A) 6.29- 1077 B) 7.70: 1077 C) 4.09- 10° D) 6.92-10°° If a sample of soditum-24 chloride contains 0.075 mg of sodium-24, how much sodium-24 remains after 9.63 hours? The half-life of sodium-24 is 14.96 hours. A) 0.027 mg B) 0.048 mg C) 0.072 mg D) 0.084 mg You order a sample of Na3PO4 containing the radioisotope phosphorus-32 (¢1/2 = 14.28 days) on Monday. You don't get to it until Thursday, 3.0 days after it was prepared and shipped. How much of the activity remains in your sample? A) 15% B) 32% C) 69% D) 87% Page 4 13. 14. Is. The gas-phase decomposition of CH3CHO (g) occurs according to the equation CH3CHO (g) ——+ CH4 (g) + CO (g) The reaction is second order with k = 0.105 M~!.s"! at 490°C. If the concentration of CH3CHO (g) is 0.022 M initially, what will its concentration be 4.3 minutes later? A) 0.0013 M B) 0.0089 M C) 0.014 M D) 0.020 M The rate law for the reaction described by the equation 2 N20 (g) ——+ 2 Nz (g) + O2 (g) is second order in N20 (g). The reaction was carried out at 900 K with an initial concentration of N2O (g) of 3.5- 10-7 M. If it took 91.3 minutes for [N20] to fall to half it original value, what is the value of the rate constant for this reaction? A) 3.5°107? M'st B) 4.8: 10° M!. - C) 5.2-103 Mls D) 84-107? M!. é The rate law for the reaction described by the equation A (g) —~ B(g) + C(g) is second order in A (g) with an rate constant k = 1.13 - 10°? M~!.s"! at 550 K. If the reaction is carried out at 550 K with an initial concentration of A (g) of 5.84 - 10° M, how long will it take for [A] to fall to half it original value? A) 1450 seconds B) 1520 seconds C) 1600 seconds D) 1920 seconds Page 5 16. How does tripling the concentration of a reactant change the rate of a reaction that is second 17. 18. 19. order in that reactant? A) The rate increases by a factor of three: (3)!. B) The rate increases by a factor of six: (2)(3). C) The rate increases by a factor of eight: (2). D) The rate increases by a factor of nine: (3). Cyclobutane, C4Hg (g), decomposes to ethylene, C2H4 (g), at 700 K: CaHs (g) ——+ 2 CoHa (g) The reaction is first order in [C4Hg] with k = 0.015 min“!. If the initial concentration of C4Hs (g) is 1.33 M, what is its concentration after 5.5 minutes? A) 0.36 M B) 0.63 M C) 0.98 M D) 12M How long does it take for the concentration of a reactant to decrease by 25.6% of its initial value for a first-order reaction with k= 1.35 min"!? A) 13.18 B) 0.200 min C) 1.01 min D) 21.9s If the half-life of uranium-238 is 4.47 - 10° years, then how long will it take for the amount of radioactivity in a sample to decrease to 0.050% of its original value? A) 5.74 half-lives B) 12.7 half-lives C) 1.93-10!° years D) 4.90- 10!° years Page 6 20. Dinitrogen pentoxide decomposes according to the reaction equation N2Os (g) ——+ 2 NO> (g) + % O2 (g) If the initial concentration of N2Os (g) is [N2O5]o = 0.832 M, and if [N2Os5] = 0.166 M at ¢ = 65.0 min, then what is [NOz2] at t= 65.0 min? A) 0.525 M B) 0.666 M C) 1.05 M D) 1.33 M 21. Incomplete initial rate data are given below for the reaction described by 22; 2 NO2 (g) ——> 2 NO (g) + O2 (g) Run [NO2]o/M | (rate ofreaction)9/ MDs! 1 1.10 0.65 2 1.60 1.38 3 2:25 x What is the rate of reaction, x, for Run 3? A) 1.53 M.s! B) 2.22 M.s"! C) 2.73 M.s"! D) 2.89 M.s"! How does halving the concentration of a reactant change the rate of a reaction that is first order in that reactant? A) The rate decreases by a factor of two: (1/2)!. B) The rate does not change: (1)!”. C) The rate increases by a factor of 1.4: (2)!/. D) The rate increases by a factor of two: (2)!. Page 7 23. If plotting your rate data as In[A] vs. ¢ results in a straight line, then which of the following represents the slope (m) of that line? A) -k B) In[{A]o C) 1/k D) 1/[A]o Page 8 Answer Key - Chapter 13 Practice Problems NON NR RR RR RR Ro NAHE SSPNAAARWNH=SOGCHNAAKRWN > FrOVOFUU WANT WTPePwBrFaanawnasa ) Y Page 9