Review 9 - Kinetics

AP chem Text: chapter 12 • • • Review - 9 (Kinetics) rate laws, integrated rate laws, graphs and half-lives energy diagrams mechanisms PROBLEMS 1. A reaction follows the rate law: rate 2 = k[A] . Which of the following plots will give a straight line? a. 1/[A] vs 1/time 2 b. [A] vs time c. 1/[A] vs time d. ln[A] vs time e. [A] vs time 2. 3. 4. 5. Name: ____________________ For the following reaction: NO2(g) + CO(g) → NO(g) + CO(g), the rate 2 law is: rate = k[NO2] . If a small amount of gaseous carbon monoxide (CO) is added to a reaction mixture that was 0.10 M in NO2 and 0.20 M in CO, which of the following statements is true? a. Both k and the reaction rate remain the same b. Both k and the reaction rate increase c. Both k and the reaction rate decrease d. Only k increases; the reaction rate remains the same e. Only the reaction rate increases; k remains the same The specific rate constant, k, for -1 radioactive beryllium-11 is 0.049 s . What mass of a 0.500 mg sample of beryllium-11 remains after 28 seconds? a. 0.250 mg b. 0.125 mg c. 0.0625 mg d. 0.375 mg e. 0.500 mg The slow rate of a particular chemical reaction might be attributed to which of the following? a. a low activation energy b. a high activation energy c. the presence of a catalyst d. the temperature is high e. the concentration of the reactants are high The steps below represent a proposed mechanism for the catalyzed oxidation of CO by O3. Step 1: NO2 + CO → NO + CO2 Step 2: NO + O3 → NO2 + O2 What are the overall products of the catalyzed reaction? a. CO2 and O2 b. NO and CO2 c. NO2 and O2 d. NO and O2 e. NO2 and CO2 6. The decomposition of ammonia to the elements is a first-order reaction with a half-life of 200 s at a certain temperature. How long will it take the partial pressure of ammonia to decrease from 0.100 atm to 0.00625 atm? a. 200 s b. 400 s c. 800 s d. 1000 s e. 1200 s 7. The energy difference between the reactants and the transition state is a. the free energy b. the heat of reaction c. the activation energy d. the kinetic energy e. the reaction energy 8. The purpose of striking a match against the side of a box to light the match is a. to supply the free energy for the reaction b. to supply the activation energy for the reaction c. to supply the heat of reaction d. to supply the kinetic energy for the reaction e. to catalyze the reaction 9. The table below gives the initial concentrations and rate for three experiments: Exp 1 2 3 [CO]o 0.200 0.100 0.200 [Cl2] 0.100 0.200 0.200 Rateo -25 3.9x 10 -25 3.9x10 -25 7.8x10 a. b. c. d. e. Rate = k[CO] 2 Rate = k[CO] [Cl2] Rate = k[Cl2] 2 Rate = k[CO][Cl2] Rate = k[CO][Cl2] 10. The reaction (CH3)3CBr(aq) + H2O(l) → (CH3)3COH(aq) + HBr(aq) follows the rate law: rate = k[(CH3)3CBr]. What will be the effect of decreasing the concentration of (CH3)3CBr? a. The rate of the reaction will increase. b. More HBr will form. c. The rate of the reaction will decrease. d. The reaction will shift to the left. e. The equilibrium constant will increase. + 11. When the concentration of H (aq) is doubled for the reaction H2O2(aq) + 2+ + 3+ 2Fe (aq) + 2H (aq) → 2Fe (aq) + 2H2O(g), there is no change in the reaction rate. This indicates that + a. the H is a spectator ion. b. the rate-determining step does + not involve H . c. the reaction mechanism does + not involve H . + d. the H is a catalyst. e. the rate law is first order with + respect to H . 12. The mechanism below has been proposed for the reaction of CHCl3 with Cl2. 1: Cl2 ⇌ 2Cl fast 2: Cl + CHCl3→CCl3 + HCl slow 3: CCl3 + Cl → CCl4 fast Which of the following rate laws is consistent with this mechanism? a. rate = k[Cl2] b. rate = k[CHCl3][Cl2] c. rate = k[CHCl3] d. rate = k[CHCl3]/[Cl2] ½ e. rate = k[CHCl3][Cl2] The reaction is CO + Cl2 → COCl2. What is the rate law? © S. O’Malley 2012 FREE-RESPONSE 13. A set of experiments were conducted to study the reaction: 2ClO2(aq) + 2OH (aq) → ClO3 (aq) + ClO2 (aq) + H2O(l). The initial concentrations and rates are reported in the table below. Exp 1 2 3 - [OH ] (M) 0.030 0.060 0.030 [ClO2] (M) 0.020 0.020 0.040 - Rate of formation of ClO3 (M/min) 0.166 0.331 0.661 a. Write the rate law of the reaction. b. Determine the value of the rate constant, including units. c. Calculate the initial rate of disappearance of ClO2 in experiment 1. d. The following mechanism has been proposed for this reaction: Step 1: ClO2 + ClO2 ⇌ Cl2O4 Step 2: Cl2O4 + OH → ClO3 + HClO2 Step 3: HClO2 + OH → ClO2 + H2O Which step is the rate-determining step? Show that the mechanism is consistent with both the rate law for the reaction and with the overall stoichiometry. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. C A B B A C C B E C B E 13. a. rate = k[ClO2]2[OH-] b. 1.4 x 104 / M2min c. -0.332 mol/L·min d. Step 1: rate = kf[ClO2]2 = kr[Cl2O4] Step 2: rate = k[Cl2O4][OH-] = k’[ClO2]2[OH-] (by substituting [Cl2O4] ∝ [ClO2]2 from the fast equilibrium in step 1) Step 3: rate = k’’[HClO2][OH-] For Step 1, the ratio of [Cl2O4] to [ClO2] is 1:2, based on the coefficients of the reaction in step 1. So the reaction in step 2 can be re-written as: 2ClO2 + OH- → ClO3- + HClO2 and the rate becomes rate = k[ClO2]2[OH-], which matches the rate law in part a. This must mean that Step 2 is the rate-determining step. Problems taken from “5 Steps to a 5”, McGraw Hill