Homework answers / question archive / Chapter 13  Kinetics: The Study of Rates of Reaction  Multiple Choice  1)Nitrogen monoxide reacts with bromine at elevated temperatures according to the equation   2 NO(g)  +  Br2(g)   →   2 NOBr(g)         In a certain reaction mixture the rate of formation of NOBr(g) was found to be 4

Chapter 13  Kinetics: The Study of Rates of Reaction  Multiple Choice  1)Nitrogen monoxide reacts with bromine at elevated temperatures according to the equation   2 NO(g)  +  Br2(g)   →   2 NOBr(g)         In a certain reaction mixture the rate of formation of NOBr(g) was found to be 4

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Chapter 13  Kinetics: The Study of Rates of Reaction

 Multiple Choice

 1)Nitrogen monoxide reacts with bromine at elevated temperatures according to the equation

 

2 NO(g)  +  Br₂(g)   →   2 NOBr(g)

        In a certain reaction mixture the rate of formation of NOBr(g) was found to be 4.50 x 10^-4 mol L^-1 s^-1.  What is the rate of consumption of Br₂(g)?

 

                                    a. 4.50 x 10^-4 mol L^-1 s^-1                    

                               b. 2.25 x 10^-4 mol L^-1 s^-1

1. 1. 1. 3. 9.00 x 10^-4 mol L^-1 s^-1 
         4. 2.12 x 10^-4 mol L^-1 s^-1
         5. 2.03 x 10^-3 mol L^-1 s^-1

 

2. Nitrogen monoxide reacts with chlorine at high temperature according to the equation, 

2 NO(g)  +  Cl₂(g)   →   2 NOCl(g)

        In a certain reaction mixture the rate of formation of NOCl(g) was found to be 4.50 x 10^-4 mol L^-1 s^-1.  What is the rate of consumption of NO(g)?

 

                         a. 4.50 x 10^-4 mol L^-1 s^-1                                      b. 2.25 x 10^-4 mol L^-1 s^-1

1. 1. 1. 3. 9.00 x 10^-4 mol L^-1 s^-1 
         4. 2.12 x 10^-4 mol L^-1 s^-1
         5. 2.03 x 10^-3 mol L^-1 s^-1

 

 

3. In a particular study of the reaction described by the equation, 

2 CH₄O(g)  +  3 O₂(g)   →   2 CO₂(g)  +  4 H₂O(g),

          the rate of consumption of O₂(g) is  0.400 mol L^-1 s^-1.  What is the rate of formation of  H₂O(g)?

 

1. 1. 1. 1. 0.300 mol L^-1 s^-1
         2. 0.400 mol L^-1 s^-1                          c. 0.533 mol L^-1 s^-1                               d. 0.800 mol L^-1 s^-1

                     e. 1.33   mol L^-1 s^-1

 

 

4. In a particular study of the reaction described by the equation, 

2 CH₄O(g)  +  3 O₂(g)   →   2 CO₂(g)  +  4 H₂O(g),

           the rate of consumption of O₂(g) is  0.400 mol L^-1 s^-1.  What is the rate of consumption of CH₄O(g)?

 

                                    a. 0.200 mol L^-1 s^-1                      b. 0.267 mol L^-1 s^-1

1. 1. 1. 3. 0.333 mol L^-1 s^-1 
         4. 0.400 mol L^-1 s^-1
         5. 0.600 mol L^-1 s^-1

 

 

5. Cyclobutane, C₄H₈, decomposes as shown: C₄H₈(g)   →   2 C₂H₄(g).  In the course of a study of this reaction, the rate of consumption of C₄H₈ at a certain point was 4.50 x 10^-4 mol L^-1 s^-1.  What is the rate at which C₂H₄(g) is being generated at this point?

 

1. 1. 1. 1. 4.50 x 10^-4 mol L^-1 s^-1
         2. 2.25 x 10^-4 mol L^-1 s^-1                          c. 9.00 x 10^-4 mol L^-1 s^-1                               d. 2.12 x 10^-4 mol L^-1 s^-1

                     e. 2.03 x 10^-3 mol L^-1 s^-1

 

 

6. The rate of a chemical reaction in solution can be measured in the units

 

   a. L² mol^-1 s^-1    b. mol L^-1 s^-1    c. s^-2

1. 1. 1. 4. mol s L^-1
         5. sec L^-1 mol^-1

 

 

7. A reaction has the rate law, rate = k[A][B]².  Which change will cause the greatest increase in the reaction rate? 

 

1. 1. 1. 1. decreasing the temperature without changing the concentrations
         2. doubling the concentration of B
         3. quadrupling the concentration of A

                   d. tripling the concentration of B

                    e. doubling the concentration of A

 

 

8. The reaction, 2 NO(g)  +  O₂(g)   →   2 NO₂(g), was found to be first order in each of the two reactants and second order overall.  The rate law is therefore

 

   a. rate = k[NO]²    b. rate = k[NO][O₂]

1. 1. 1. 3. rate = k[NO₂]²[NO]^-2[O₂]^-½
         4. rate = k[NO]²[O₂]²
         5. rate = k([NO][O₂])²

 

 

9. A reaction has the rate law, rate = k[A][B]².  What is the overall order of the reaction? 

 

1. 1. 1. 1. 2nd
         2. 4th
         3. 1st    d. 3rd    e. 0

 

 

10. A reaction has the rate law, rate = k[A][B]².  What is the order of the reaction with respect to B? 

 

   a. 2nd    b. 4th

1. 1. 1. 3. 1st
         4. 3rd
         5. 0

 

 

11. For the reaction, 2 XO  +  O₂   →   2 XO₂, data obtained from measurement of the initial rate of reaction at varying concentrations are given below.  

                                                    Experiment       [XO]           [O₂]      Rate (mmol L^-1 s^-1 )

1. 1. 1. 1. 1. 1. 1. 1. 0.010      0.010           2.5
                     2. 0.010      0.020           5.0
                     3. 0.030      0.020         45.0

     The rate law is therefore                                                   

                         a. rate = k[XO]² [O₂]                                      b. rate = k[XO][O₂]²

1. 1. 1. 3. rate = k[XO][O₂]
         4. rate = k[XO]² [O₂]²
         5. rate = k[XO]²/[O₂]²

 

 

12. For the reaction, 2 M  +  2 N   →   2 P  +  Q, studies on how the initial rate of the reaction varied with concentration were carried out.  Some data is given below.

 

Experiment	[M]     [N]       Rate (mol L-1 s-1 )
1	0.100  0.100      0.000230
2	0.100  0.200      0.000920
3	0.200  0.200      0.000920

 

                   a. the rate law is therefore: rate = k[N]²

1. 1. 1. 2. the rate law is therefore: rate = k[M][N]²
         3. the rate law is therefore: rate = k[M][N]
         4. the rate law is therefore: rate = k[M]²
         5. the rate law is therefore: rate = k[M]²[N]² 

 

 

13. For the reaction, A  +  2B   →  C  +  2 D, the following data were obtained                                            

 

                                                         Experiment          [A]     [B]        Rate (mol L^-1 s^-1 )

1. 1. 1. 1. 1. 1. 1. 1. 0.100  0.200      0.000360
                     2. 0.200  0.200      0.000720                                                           3                 0.100  0.400      0.000720

 

1. 1. 1. 1. the rate law is therefore: rate = k[A][B]²
         2. the rate law is therefore: rate = k[B]
         3. the rate law is therefore: rate = k[A]                      d. the rate law is therefore: rate = k[A][B]

                     e. the rate law is therefore: rate = k[A]²[B]

 

 

14. For the reaction, A  +  2 B   →  C  + 2 D, some measurements of the initial rate of reaction at varying concentration gave the following data.

 

                                                        Experiment   [A]       [B]        Rate (mol L^-1 s^-1 )

1. 1. 1. 1. 1. 1. 1. 1. 0.100   0.200      0.000360
                     2. 0.150   0.200      0.000540                                                         3                0.150   0.250      0.001055

 

1. 1. 1. 1. the rate law is therefore: rate = k[A]²[B]
         2. the rate law is therefore: rate = k[A][B]²
         3. the rate law is therefore: rate = k[A]²[B]²
         4. the rate law is therefore: rate = k[A][B]                 e. the rate law is therefore: rate = k[A][B]³

 

 

15. Nitric oxide reacts with bromine at elevated temperatures according to the equation 

2 NO(g)  +  Br₂(g)   →   2 NOBr(g)

       The experimental rate law is rate = k[NO][Br₂].  In a certain reaction mixture the rate of formation of NOBr(g) was found to be 4.50 x 10^-4 mol L^-1 s^-1.  Which unit below is the correct unit for the rate constant in this case?

 

1. 1. 1. 1. mol L^-1 s^-1
         2. s^-1
         3. mol² L^-2 s^-1

                   d. mol^-1 L s^-1

                     e. mol^-2 L² s^-1

 

 

16. For the reaction, 3 B  +  C   →   E  +  2 F, initial rate measurements were carried out and data for three runs are shown below

                                                      Experiment      [B]      [C]       Rate (mol L^-1 s^-1 )

1. 1. 1. 1. 1. 1. 1. 1. 0.100   0.250      0.000250
                     2. 0.200   0.250      0.000500
                     3. 0.100   0.500      0.00100              The rate law, therefore, is 

 

1. 1. 1. 1. rate = k[B]³[C]
         2. rate = k[B][C]
         3. rate = k[B]²[C]²
         4. rate = k[B]²[C]    e. rate = k[B][C]²

 

 

17. The reaction, 2 A₂X₄(g)   →   2 A₂X₃(g)  +  X₂(g), was found to be first order.  The rate law, therefore, should be 

 

1. 1. 1. 1. rate = k([A₂X₃]²[X₂])/[A₂X₄]²
         2. rate = k[A₂X₄]²
         3. rate = k([A₂X₃][X₂])/[A₂X₄]

                   d. rate = k[A₂X₄]

                     e. rate = k[A₂X₄]²/([A₂X₃]²[X₂])

 

 

18. Given the reaction, 

aA+bB??→dD+eE

 

        If we try rate =  k[A]^q[B]^r  for a generic rate law statement, which one of the statements below is false?

 

1. 1. 1. 1. The exponents q and r are often integers.
         2. The exponent q and r must be determined experimentally.

                         c. The exponents q and r are equal to the coefficients a and b, respectively.                                      d. The overall order of the reaction is q + r.   

                     e. The symbol k represents the rate constant.

 

 

19. The reaction, A  +  2 B   →  products, was studied.  The reagents A and B were mixed and the time interval until a certain quantity of product C accumulated was measured.  The data were obtained

 

                                                          Experiment    [A]      [B]      Time (secs)

1. 1. 1. 1. 1. 1. 1. 1. 1. 0.100   0.140        25
                        2. 0.050   0.140        50
                        3. 0.100   0.070      100

        We can conclude that

 

                   a. the reaction is first order with respect to substance A

1. 1. 1. 2. the reaction is zero order with respect to substance A 
         3. the reaction is one-half order with respect to substance A
         4. the reaction is second order with respect to substance A
         5. the reaction is third order with respect to substance B

 

 

20. The data below were obtained in a study on how the rate of a reaction was affected by the concentration of its reactants.

 

                                               Experiment   [A]       [B]      [C]     Rate (mol L^-1 hr^-1)

1. 1. 1. 1. 1. 1. 1. 0.200   0.100   0.600           5.0
                  2. 0.200   0.400   0.400          80.0
                  3. 0.600   0.100   0.200          15.0
                  4. 0.200   0.100   0.200           5.0
                  5. 0.200   0.200   0.400          20.0

        From this data 

 

1. 1. 1. 1. The order of the reaction with respect to C cannot be determined.
         2. The reaction is second order with respect to C.                     c. The reaction is zero order with respect to C.                          d. The reaction is first order with respect to C.

                     e. The order of the reaction with respect to C is minus one.

 

 

21. Given these data in a study on how the rate of a reaction was affected by the concentration of the reactants,

 

                                             Experiment   [A]       [B]       [C]     rate, mol L^-1 hr^-1

1. 1. 1. 1. 1. 1. 1. 0.200    0.100   0.600     5.0
                  2. 0.200    0.400   0.400   80.0
                  3. 0.600    0.100   0.200   15.0
                  4. 0.200    0.100   0.200     5.0
                  5. 0.200    0.200   0.400   20.0

        From this data

 

1. 1. 1. 1. the reaction is zero order with respect to B.
         2. the reaction is first order with respect to B.
         3. the reaction order for B cannot be determined.                       d. the reaction is second order with respect to B.                                 e. the reaction order for B is minus one.

 

 

22. Given these data in a study on how the rate of a reaction was affected by the concentration of the reactants,

 

                                              Experiment   [A]       [B]       [C]     Rate (mol L^-1 hr^-1 )

1. 1. 1. 1. 1. 1. 1. 0.200   0.100   0.600      5.0
                  2. 0.200   0.400   0.400    80.0
                  3. 0.600   0.100   0.200    15.0
                  4. 0.200   0.100   0.200      5.0
                  5. 0.200   0.200   0.400    20.0

        From this data

 

                   a. the reaction is first order with respect to A. 

1. 1. 1. 2. the reaction is second order with respect to A.
         3. the reaction is zero order with respect to A.
         4. the reaction order for A is minus one (Rate proportional to 1/[A]). 
         5. the reaction order for A cannot be determined from just this data alone.

 

 

23. If a reaction involving a single reactant is first order with a rate constant of 4.50 x 10^-2 s^-1, how much time is required for 75.0% of the initial quantity of reactant to be used up?

 

   a. 16.7 seconds    b. 30.9 seconds    c. 23.1 seconds

1. 1. 1. 4. 25.3 seconds
         5. 11.6 seconds

 

 

24. For a first order reaction with a single reactant, after 230.0 seconds, 10.0% of the reactant remains.  The rate constant for the reaction is therefore 

 

   a. 0.000640 s^-1    b. 0.0100 s^-1    c. 100 s^-1

1. 1. 1. 4. 0.0510 s^-1
         5. 0.0915 s^-1

 

The graphs listed below refer to questions 25 - 29

 

 

 

 

 

Sections 13.2, 13.3, 13.4

 

25. Graph a can best be described as                   a. Zero order rate process.
    1. 1. 2. First order rate process.
          3. Second order rate process.
          4. b or c
          5. a or c

 

26. Graph b can best be described as
    1. 1. 1. Zero order rate process.
          2. First order rate process.
          3. Second order rate process.                   d. b or c                                  e. a or c

 

27. The instantaneous rate at any point in graph b can be found by
    1. 1. 1. taking the average of all rates found every 100 s
          2. drawing a line tangent to the curve at the initial and final times, and then averaging

                  c. drawing a line tangent to the curve at that point

1. 1. 1. 4. subtracting the final concentration from the initial concentration and dividing by the time interval
         5. subtracting the final time from the initial time and dividing by the concentration

 

28. The average rate over a time period in graph b can be found by
    1. 1. 1. taking the average of all rates found every 100 s
          2. drawing a line tangent to the curve at the initial and final times, and then averaging
          3. drawing a line tangent to the curve at that point

   d. subtracting the final concentration from the initial concentration and dividing by the time interval

                    e. subtracting the final time from the initial time and dividing by the concentration interval

 

29. We can determine the reaction order from graph b by
    1. 1. 1. doing nothing
          2. plotting 1/[A] vs. time and getting a straight line
          3. plotting ln[A] vs. time and getting a straight line
          4. plotting the square root of concentration vs. time and getting a straight line

                  e. b and c

 

 

30. In a first order reaction with only one reagent, the reaction was started with a concentration of reactant equal to 0.0800 M.  After exactly two hours, the concentration had fallen to 0.0400 M.  What is the molarity after exactly four hours?

 

1. 1. 1. 1. 0.0000 M
         2. 0.0100 M
         3. 0.0150 M    d. 0.0200 M    e. 0.0300 M

 

 

31. In a first order reaction with only one reagent, the reaction was started with a concentration of reactant equal to 0.0800 M.  After exactly two hours, the concentration had fallen to 0.0400 M.  What is the molarity after exactly six hours?

 

   a.  0.0000 M    b. 0.0100 M    c. 0.0150 M

1. 1. 1. 4. 0.0200 M
         5. 0.0300 M

 

 

32. The half-life of a chemical reaction was found to be independent of the quantity of reactant which was employed.  The reaction is therefore 

 

   a. possibly first order    b. definitely first order    c. zero order

1. 1. 1. 4. possibly second order
         5. definitely second order 

 

 

33. The decomposition of an aldehyde solution in carbon tetrachloride is a first order reaction with a rate constant of 1.20 x 10^-3 min^-1.  If we start with [aldehyde] = 0.0500 M, what will the concentration be 150 minutes later?

 

                     a. 0.00900 M

                   b. 0.0418 M

                                     

1. 1. 1. 3. 0.00926 M
         4. 0.00499 M
         5. 0.000333 M

 

 

34. The rate constant for a first order decomposition reaction is 0.0111 min^-1.  What is the half-life of the reaction?

 

   a. 111 min    b. 62.4 min    c. 5000 sec

1. 1. 1. 4. 31.25 min
         5. 27.1 min

 

 

35. Given a reaction, 2 A  +  B   →   P, for which the rate law is rate = k[A].  Which equation or statement is true?

 

1. 1. 1. 1. [A] = 1/kt
         2. ln[A] = k/t
         3. 1/[A] = kt

                         d. the half-life is 0.693/k                                 e. e^[A] = -kt

 

 

36. In a first order reaction, what fraction of the reactant will remain after 4 half-lives?

 

   a. 1/16                                                       b. 1/8                                                   

1. 1. 1. 3. 1/9                                                   
         4. 1/4                                                   
         5. 1/3                                                   

 

 

37. The initial concentration of a reactant in a first order reaction is 0.620 M.  What will be its concentration after 3 half-lives? 

 

1. 1. 1. 1. 0.0865 M
         2. 0.310 M    c. 0.0775 M    d. 0.103 M

                     e. 0.207 M

 

 

38. For the reaction, A   →   B  +  C, the rate law is rate = k[A].  If it takes 80.0 seconds for 70.0% of a

10.0 gram sample of A to be transformed into products, what is the value of the rate constant?

 

1. 1. 1. 1. 0.00450 s^-1                                         
         2. 0.0290 s^-1                                           
         3. 0.00530 s^-1                                             d. 0.0150 s^-1                                              e. 5.40 s^-1                                            

 

 

39. The reaction of substance A with substance C was carefully studied under conditions where the [C] remained essentially constant.  The graphs of [A] vs. time and that of ln[A] vs. time both gave curves, but the graph of 1/[A] vs. time gave a straight line. 

 

1. 1. 1. 1. The reaction is therefore zero order with respect to A.
         2. The reaction is therefore one-half order with respect to A.
         3. The reaction is therefore first order with respect to A.                  d. The reaction is therefore second order with respect to A.

                    e. The reaction is therefore third order with respect to A.

 

 

40. The reaction of substance A with substance C was carefully studied under conditions where the [C] remained essentially constant.  The graph of [A] vs. time gave a straight line while the graph of ln[A] vs. time and that of 1/[A] vs. time both gave curves. 

 

                   a. The reaction is therefore zero order with respect to A.

1. 1. 1. 2. The reaction is therefore one-half order with respect to A.
         3. The reaction is therefore first order with respect to A.
         4. The reaction is therefore second order with respect to A.
         5. The reaction is therefore third order with respect to A.

 

 

41. A reaction is first order overall.  For a given sample, its initial rate is 0.0200 mol L^-1 s^-1 and 25.0 days later its rate dropped to 6.25 x 10^-4 mol L^-1 s^-1. What is its half-life?

 

1. 1. 1. 1. 25.0 days
         2. 50.0 days
         3. 12.5 days

                  d. 5.0 days

                    e. 37.5 days                                                                                

 

 

42. A first order reaction has a rate constant of 0.00318 min^-1.  The half-life of this reaction is therefore

 

                     a. 94.7 minutes

                   b. 218 minutes

1. 1. 1. 3. 31.4 minutes
         4. 5.24 seconds
         5. 68.6 minutes

 

 

43. For a one step reaction, the activation energy for the forward reaction is 40.0 kJ mol^-1, and the enthalpy of reaction is -20.0 kJ mol^-1.  Which statement below is true? 

 

1. 1. 1. 1. The activation energy of the forward reaction would be affected to a greater extent                                     than the activation energy of the reverse reaction by addition of a catalyst. 
         2. The value for the enthalpy of reaction would be decreased by addition of a catalyst.
         3. The reaction is endothermic.

                   d. The reverse reaction has a higher activation energy than the forward reaction.

                     e. The reaction rate would be decreased by an increase in temperature. 

 

44. A variable which has no effect on the rate of a chemical reaction under any circumstances is

 

1. 1. 1. 1. energy of activation.
         2. a catalyst. 
         3. the concentration of the reactants.
         4. the temperature.

                  e. the standard enthalpy of reaction for the system. 

 

 

45. For a one step reaction, the activation energy for the forward reaction is 40.0 kJ mol^-1, and the enthalpy of reaction is -20.0 kJ mol^-1.  Calculate the activation energy for the reverse reaction.

 

   a. +60.0 kJ mol^-1    b. -20.0 kJ mol^-1

1. 1. 1. 3. -1200 kJ kJ mol^-1
         4. +20.0 kJ kJ mol^-1
         5. +1200 kJ kJ mol^-1

                                                                                

 

46. For a chemical reaction, the rate constant at 250.0 ^°C is 0.00383 s^-1, and the activation energy is

22.40 kJ mol^-1.  Calculate the value of the rate constant at 335.0 ^°C.

 

1. 1. 1. 1. 0.00513 s^-1
         2. 0.00946 s^-1    c. 0.00787 s^-1    d. 0.0224 s^-1

                     e. 0.000640 s^-1

 

 

47. For a chemical reaction, the rate constant at 42.0 ^°C is 0.00395 s^-1, while the rate constant at 67.4 ^°C is 0.0133 s^-1.  Calculate the value of the energy of activation, in kilojoules per mole.

 

   a. 42.65    b. 1.13

1. 1. 1. 3. 0.421
         4. 18.5
         5. 0.617

 

 

48. The rate constant for a certain chemical reaction is 0.00250 L mol^-1 s^-1 at 25.0 C and 0.0125 L mol^-1 s^-1 at 50.0 ^°C.  What is the activation energy for the reaction, expressed in kJ mol^-1?

 

   a. 25.1 kJ mol^-1    b. 51.6 kJ mol^-1    c. 37.6 kJ mol^-1

1. 1. 1. 4. 45.3 kJ mol^-1
         5. 60.3 kJ mol^-1

 

 

49. For a particular chemical reaction, the rate constant at 30.0 ^°C is 1.38 x 10^-4 L mol^-1 s^-1, while the value at 0 ^°C is 1.21 x 10^-3 L mol^-1 s^-1.  What is the activation energy for this reaction?

 

   a. 92.8 kJ                                                    b. 200 kJ                                                 

1. 1. 1. 3. 40.4 kJ                                                
         4. 343 kJ                                                 
         5. 56.4 kJ

 

 

50. The activation energy for a reaction can be found by finding the slope of a plot of ln(k) vs. T^-1 and

 

1. 1. 1. 1. adding this slope to –R.
         2. multiplying this slope by 2.303.
         3. dividing this slope by –R.
         4. multiplying this slope by 2.303R.

                   e. multiplying this slope by –R.

 

 

51. The reaction:  A  +  3 B   →   D  +  F  was studied and the following mechanism was determined

                                                             

 

                                 A  +  B 

 C                 (fast)

 

                                                                                                                                                                         C  +  B   →   D  +  E                 (slow)

                                 E  +  B   →   F                    (very fast)

 

        The step with largest activation energy is                                

                                                                                

   a. the first step    b. the second step    c. the third step

1. 1. 1. 4. none of the steps has an activation energy
         5. all of the steps have the same activation energy

 

 

52. Suppose the reaction:  A  +  B   →   D  followed the mechanism 

 

                                 A  +  B   C         (fast)

                                                                                                   

                                 C   →   D             (slow)

 

The rate law for the reaction would be

 

1. 1. 1. 1. rate = k[A]
         2. rate = k[A]²    c. rate = k[A][B]

1. 1. 1. 4. rate = k[A][B]/[D]
         5. rate = k[A][B][C]

 

 

53. The reaction:  A  +  3 B   →   D  +  F was studied carefully and the following mechanism was finally determined.

 

                                  A  +  B   C                 (fast)

                                                                                                  

                                C  +  B   →   D  +  E          (slow)

                                 E  +  B   →   F                    (very fast)

 

The rate law for the reaction would therefore be

 

   a. rate = k[A]²[B]     b. rate = k[A][B]²    c. rate = k[C][B]

1. 1. 1. 4. rate = k[A][B]³
         5. rate = k[A][B]

 

 

54. Which statement about the slow step in the mechanism for a reaction mechanism is true?

 

1. 1. 1. 1. It has a rate that is independent of the activation energy for the reaction.
         2. It limits the effectiveness of a catalyst.

                  c. It controls the rate at which the products are produced.

1. 1. 1. 4. It almost always involves the breaking of hydrogen bonds.
         5. It determines the value of the standard enthalpy of reaction for the reaction.

 

55. The reaction mechanism proposed for the decomposition of H₂O₂ is

 

                                 H₂O₂  +  I^-   →   H₂O  +  IO^-             (slow)

                                H₂O₂  +  IO^-   →   H₂O  + O₂  +  I^-    (fast)

 

     Which statement is true?

 

1. 1. 1. 1. The reaction is second order with respect to I^-.
         2. I^- is an intermediate.

                         c. The reaction is first order with respect to I^-.                                      d. IO^- is a catalyst.

                     e. The reaction is zero order with respect to I^-.

 

 

56. If the reaction, H₂(g)  +  Cl₂(g)   →   2 HCl(g) occurred in just two steps what would the overall order of the reaction be?

 

1. 1. 1. 1. 1st
         2. 2nd
         3. 3rd
         4. 4th

                   e. It is impossible to determine the order from this limited information.                                

 

57. Which statement concerning the rate of a chemical reaction is false? 

 

                         a. It will be very rapid if the activation energy is large.                                 b. It will be slow if one or more of the steps is slow.

1. 1. 1. 3. It may be inhibited sometimes by certain catalytic agents.
         4. It is dependent on temperature.
         5. It often increases when the concentrations of one of the reactants is increased.

 

58. A chemical reaction has been the subject of intense study, and a rate law,  rate = k[A][B]², was developed which summarized the mechanistic findings.  Which change to the system will not cause an increase in the rate constant under any circumstances? 

 

1. 1. 1. 1. raising the temperature by 25 degrees
         2. adding a positive catalyst
         3. adding a negative catalyst                          d. doubling the concentration of B

                    e. lowering the temperature by 0.5 degrees

 

59. The reaction, A  +  3 B   →   D  +  F was studied and the following mechanism was established:

 

                                  A  +  B   C                 (fast)

                                                                                                  

                                C  +  B   →   D  +  E          (slow)

                                 E  +  B   →   F                    (very fast)

 

        The species, E, is properly described as

 

   a. an intermediate.    b. a co-factor.

1. 1. 1. 3. a catalyst.
         4. an inhibitor.
         5. an enzyme.

 

60. The reaction:  A  +  3 B   →   D  +  F  was studied and the following mechanism was determined.

                                                             

                                  A  +  B    C                (fast)

                                          C  +  B   →   D  +  E          (slow)

                                 E  +  B   →   F                    (very fast)

        The species, C, is properly described as

 

1. 1. 1. 1. a co-factor.
         2. an inhibitor. 
         3. a catalyst.
         4. an enzyme.

                   e. an intermediate.

 

 

61. A catalyst alters the rate of a chemical reaction by

 

                         a. providing an alternate pathway which has a different activation energy.                                      b. changing the products formed in the reaction.

1. 1. 1. 3. changing the frequency of collisions between molecules.
         4. always providing a surface on which molecules react.
         5. changing the enthalpy of reaction for the reaction.

 

 

62. Which statement is true concerning a negative catalyst?

 

1. 1. 1. 1. It lowers the energy of activation of the rate determining step.
         2. It increases the enthalpy of reaction. 
         3. It never undergoes a chemical change at any time during a chemical reaction.
         4. It blocks the path with the highest energy of activation for the rate determining step.           e. It blocks the path with the lowest energy of activation for the rate determining step.

 

63. Which statement describes the situation when a positive catalyst is used in a reaction? 

 

1. 1. 1. 1. The forward reaction rate is increased while the reverse reaction rate is retarded.
         2. The enthalpy change for the reaction becomes more exothermic.

                         c. The final (equilibrium) amounts of reactants and products are not affected.                                 d. The activation energy for the reverse reaction is increased.

                    e. The activation energy for the forward reaction is not altered.

 

 

Fill in the Blanks

 

 

64. The decomposition of a compound is known to be a first order reaction.  If the half-life of the reaction is 6.25 minutes at 65 ^°C, what is the value of the rate constant for the reaction at this temperature?  ________

 (0.1109 min^-1)

 

 

65. The nuclear transmutation reaction of X  is a first order reaction.  If the half-life of X is 188.5 hours, how much would a sample weighing 14.55 mg today weigh at the same time tomorrow?  __________

(13.32 mg)

 

 

66. An isomerization reaction of a substance, A,  is first order.  In a laboratory class one student group found that 28.5% of A had isomerized after a period of 15.0 minutes when the temperature was maintained at 84.5 ^°C.  What is the half-life of substance A at that temperature?  _______

(31.0 minutes)

 

 

66. What effect does the magnitude of the standard enthalpy of reaction have on the rate constant for a reaction, if the temperature is kept constant?  ____________

 (no effect)

 

 

67. What effect does a negative catalyst have on the value of the rate constant for a particular reaction?  ____________

 (It causes the value to decrease)

 

 

True and False

 

 

68. If increasing the concentration of a particular reactant in a reaction mixture by a factor of three fails to cause any measurable change in the rate of a chemical reaction, the order of reaction with respect to that particular reactant is zero.  ___

   

 

 

69. Nitric oxide reacts with bromine at elevated temperatures according to the equation, 

2 NO(g)  +  Br₂(g) →   2 NOBr(g).

        The experimental rate law is: rate = k[NO][Br₂].  The half-life of either of the reactant species is independent of its concentration and is equal to 0.693/k.  ___

  

 

 

70. The activation energy is the energy required to initiate a reaction, and the reaction will continue without further outside assistance.  ___ 

 

 

 

71. The activation energy of a reaction is equal to the difference between the standard enthalpy of formation of the reactants and the standard enthalpy of formation of the products.  ___

  

 

 

72. The activation energy of a reaction is equal to the difference between the activation energy for the forward step of the reaction and the standard enthalpy of formation of the reactants.  ___

  

 

 

73. A catalyst that lowers the activation energy of the forward reaction in a system to one-half its uncatalyzed value will also lower the activation energy of the reverse reaction in the system to one-half its uncatalyzed value.  ___ 

 

 

 

74. The rate law of an elementary step uses the coefficients of the balanced equation describing it as its exponents. ____

  

 

 

75. The final step in a multistep reaction mechanism is the rate determining step.  ___ 

 

 

 

 

76. The final step in a multistep reaction mechanism is the net reaction.  ___ 

 

 

 

77. In order to carry out chemical kinetics studies, all reactants must be in a catalyzed form so that they will form products at the regular rate.  ___

   

 

Critical Thinking Questions

 

 

78. Given this data from a study on how the rate of a reaction was affected by the concentration of the reactants

                                                                                                                              

                                                Experiment    [A]       [B]      [C]     Initial rate (mol L^-1 hr^-1)

1. 1. 1. 1. 1. 1. 0.200   0.100   0.600       5.0
               2. 0.200   0.400   0.400      80.0
               3. 0.600   0.100   0.200      15.0
               4. 0.200   0.100   0.200       5.0
               5. 0.200   0.200   0.400      20.0

 

                         a. the rate constant is 2500 L² mol^-2 hr^-1                                 b. the rate constant is 208 L² mol^-2 hr^-1

1. 1. 1. 3. the rate constant is 139 L² mol^-2 hr^-1
         4. the rate constant is 2083 L² mol^-2 hr^-1
         5. the rate constant is 6667 L² mol^-2 hr^-1

 

 

79. A nuclear transmutation reaction is a first order reaction.  The mass of a sample was taken on three successive days at the same time.  First day:  14.554 mg.    Second day:  14.193 mg.   Third day: 

13.841 mg.   What should the mass be at the same time on the fifth day?  ______ 

ANS: (13.163 mg)

 

 

80. The reaction,  2 NO₂(g)   ??→ 2 NO(g)   + O₂(g), has a rate constant of 0.110 L mol^-1 s^-1 when the temperature is 450 ^°C.  How long, in seconds, would it take for a sample of NO₂ whose concentration is initially 0.355 M to decrease to 25.0 % of its original concentration at this temperature?  _______

ANS:  (76.8 s)

 

 

81. The half-life of a first order chemical reaction is 24.0 minutes at 55.0 C and 16.4 minutes at 63.5 ^°C.  What will be the half-life, in minutes, at 70.0 ^°C?______

ANS:  (12.4 minutes)

 

 

82. The decomposition of hydrogen peroxide in solution was studied in the laboratory, and the following mechanism was proposed based on the experimental data.  

 

                                 H₂O₂  +  I^-   →   H₂O  +  IO^-              (slow)

                                H₂O₂  +  IO^-   →   H₂O  + O₂  +  I^-     (fast)

 

        Which one of the following statements is false?                                      

 

1. 1. 1. 1. The reaction is first order with respect to H₂O₂.
         2. The reaction is first order with respect to I^-.
         3. I^- is a catalyst.
         4. IO^- is an intermediate.

                   e. The reaction is first order with respect to IO^-.

 

 

83. Suppose the reaction,  2 A  + 2 B   →   2 D  +  F   followed the mechanism

 

                                  A  +  B     C  +  D   (fast)

                                A  +  C   →   E                   (slow)

                                E  +  B   →   D  +  F           (very fast)

 

The rate law for the reaction would be

 

                         a. rate = k[A]²[B] / [D]                                      b. rate = k[A][B][C]

1. 1. 1. 3. rate = k[A][B]/[D]
         4. rate = k[A]²[B]²
         5. rate = k[A][B]²

 

 

Short answers

 

84. Heterogeneous catalysis often takes place at transition metal surfaces. Which would be a better choice for a catalyst—a gold sphere with a radius of 18Å, or 15 gold spheres, each with a radius of 5 Å? Hint: The surface area of a sphere is given by: A = 4πr². 

 

 

85. Describe, in words, the effects of a catalyst on a chemical reaction. 

 

 

86. What is the difference between the average and instantaneous rates of a reaction? 

 

 

87. What is the difference between homogenous and heterogeneous catalysis? 

 

 

88. Why does increasing the temperature of a reaction mixture increase the reaction rate? 

 

 

89. What are the factors which determine the rate of a chemical reaction?