Chemical Kinetics Practice Test - Answer Key

 

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  1. When 0.52 g of H2 and 0.19 g of I2 are confined to a 750. mL vessel heated to 700. K, they react by a second order process (first order in each reactant), with k = 0.063 L mol -1 s -1 in the rate law ( for the rate of formation of HI). 
    • What is the initial reaction rate?

      Rate = 2.16 x 10-4 mol L-1s-1

      •  

    • By what factor does the reaction increase if the concentration of H2 present in the mixture double?

      Double the rate.

     

     

  2. The following rate data were collected for the reaction

    2 A(g) + 2 B(g) + C(g)     → 3G(g) + 4 F(g)­


      3.  

    • What is the order for each reactant and the overall order of the reaction?

      A = 1              B = 2               C = 0               overall order = 3

      •  

    • Write the rate law for the reaction?

      Rate = k[A][B]2

      •  

    • Determine the reaction rate constant.

      k = 2.0 x 10-5 L2 mol-2 s-2

     

     

  3. Predict the initial rate for Experiment 5.

    Rate5 = 2.9 x 10-6 mol L-1 s -1 

    4.  

     

  4. A first order reaction is 38.5% complete in 480 s.
    • Calculate the rate constant.

      k = 1.01 x 10-3 s-1

      •  

    • What is the value of the half-life?

      686.3 s

      •  

    • How long will it take for the reaction to be 75.0% complete?

      1372.6 s

     

     

  5. One pathway for the destruction of ozone in the upper atmosphere is

    Step 1                        O3 + NO     → NO2 + O2
    Step 2                        NO2 + O     → NO + O2

      6.  

    • Write the overall reaction.

      O3 + O       à 2 O2

      •  

    • What are the reaction intermediates?

      NO2

      •  

    • What are the catalysts?

      NO
  6. A proposed mechanism for a reaction is:

    C4H9Br     → C4H9+ + Br -                                Slow
    C4H9+ + H2O     → C4H9OH2+                         Fast
    C4H9OH2+ + H2O     → C4H9OH + H3O+       Fast

    Write the rate law expected for this mechanism?

    Rate = k[C4H9Br]

    7.  

     

  7. Consider:

    2CH3OH(g) + 3O2 (g)     → 2CO2 (g) + 4H2O (l)

    At certain temperatures it obeys the rate law:

    Rate = 5.30 M -1 s -1 [CH3OH]2

    Suppose a vessel contains CH3OH at a concentration of 1.83 M.  Calculate the concentration of the CH3OH in the vessel 0.968 seconds later.

    [CH3OH] = 0.176 M

    8.  

     

  8. If the rate law was determined to be

    Rate = k[A]-0.8[B]3.1

    What are the units for k?

    L1.3 mol-1.3 s-1

    9.  

     

  9. What is the 2nd half-life for a reaction with k = 15 M -1 s‑1 and an initial concentration of 16M?

    0.0083 s

    10.  

     

  10. The reaction profile for the mechanism

    NO2 (g) + F2 (g)     → NO2F(g) + F (g)    Slow
    F­ (g) + NO2     → NO2F (g)                    Fast

    Shows

      11.  

    • 2 maxima, the second maximum being higher than the first

      •  

    • One maximum for the first step

      •  

    • 2 maxima of the same heights

      •  

    • One maximum for the second step

      •  

    • 2 maxima, the first one higher than the second one.

     

     

  11. The rate constant of the first order reaction

    2 N2O (g)     → 2 N2 (g) + O2 (g)

    is 0.76 s -1 at 1000. K and 0.87 s -1 at 1030 K.  Calculate the activation energy of the reaction.

    Ea = 38,585 J

    12.  

     

  12. Complete the following statements relating to the following overall reaction:

     

    N2 (g) + 3H2 (g)     → 2NH3 (g)

      13.  

    • The rate of  N2 is -1/3 times the rate of consumption of H2.

      •  

    • The rate of formation of NH3­ is -2/3  times the rate of consumption of H2.

      •  

    • The rate of formation of NH3 is -2 times the rate of consumption of N2.

     

     

  13. The first order reaction A → 3B + C, when [A]o =0.015 M, the concentration of B increases to 0.018 M in 3.0 min.

      14.  

    • What is the rate constant for the reaction expressed as a rate loss of A?

      k = 2.84 x 10-3 s-1

      •  

    • How much more time would be needed for the concentration of B to increase to 0.030 M?

      6.45 min

     

     

  14. Determine the rate law for the following reaction

    Cl2 (g) + CHCl3 (g)     →  HCl(g) + CCl4 (g)

    Given the following mechanism:

    Cl2 (g)  2Cl (g)                                                              Fast Equilibrium
    Cl (g) + CHCl3 (g)     →  HCl (g) + CCl3 (g)             Slow
    CCl3 (g) + Cl (g)     → CCl4 (g)                             Fast

    Rate = k[Cl2]1/2[CHCl3]

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