Chemical Kinetics

chemistry

Chemical Kinetics: Problem Set A (Measuring Reaction Rates & Rate Laws)

 

 1.            What are the relative rates for each reactant and product in the decomposition of nitrosyl chloride (NOCl)?  The reaction is:

                        2NOCl  ®  2NO  +  Cl₂

2.      What would be the rate of formation of CO₂ if the concentration of octane, C₈H₁₈ was changing at a rate of 0.25 mol L^-1 s^-1 during the combustion of octane?

3.      When the concentration of a particular reactant was increased by a factor of 10, the reaction rate was increased by a factor of 1000. What is the order of the reaction with respect to that reactant?

4.            A certain reactant disappears by a first-order reaction that has a rate constant           k = 3.5 x 10^-3 s^-1. If the initial concentration of the reactant is 0.500 M, how long will it take for the concentration to drop to 0.200 M?  

5.            Can vegetarians eat animal crackers?

6.            A certain first-order reaction has a half-life of 30 minutes. What is the rate constant for the reaction?

7.            In dilute NaOH at 20 °C, the decomposition of hydrogen peroxide (H₂O₂) is first-order in H₂O₂ only, and the rate constant is 1.00 x 10^-3 min^-1. If the initial concentration of H₂O₂ is 0.020 M, what is its concentration after exactly 100 minutes?

8.            The reaction

                  2NO_(g)      +     Cl_2(g)    ®  NOCl_(g)

   was studied at -10°C. The following results were obtained where rate = - D[Cl₂]/Dt

                                         

[NO]0 (M)	[Cl2]0 (M)	Initial rate (M.min-1)
0.10	0.10	0.18
0.10	0.20	0.36
0.20	0.20	1.45

a)      What is the rate law?

b)      What is the value of the rate constant?

9.            A dimer is a molecule composed of two identical molecules. Butadiene (C₄H₆) reacts to form its dimer according to the equation:

                        2C₄H_6(g)   ®    C₈H_12(g)

         The following data were collected for this reaction at a given temperature:

                       

[C4H6] (M)	Time (s)
0.01000	0
0.00625	1000
0.00476	1800
0.00370	2800
0.00313	3600
0.00270	4400
0.00241	5200
0.00208	6200

a)      Is this reaction first-order or second-order? (HINT: Plot a graph)

b)      What is the value of the rate constant for the reaction?

c)      What is the half-life for the reaction under the conditions of this experiment?

10.        The reaction

                        2HI ® H₂  +  I₂ 

         is second-order with respect to HI. At 508°C, k = 0.079 L mol^-1 s^-1.

a)      Write the rate law for this reaction.

b)      What is the half-life for this reaction at 508°C when initially [HI] = 0.050M?

Answers:

1.            rate = -1/2D[NOCl]/Dt = 1/2D[NO]/Dt = D[Cl₂]/Dt

2.            2.0 mol L^-1 s^-1                  3.    3^rd order               4.  2.6 x 10² s               5.  laugh!

6.      3.8 x 10^-4 s^-1                   

7.      0.018 M             

8.      a) rate = k[NO]²[Cl₂]                b) 1.8 x 10² L² mol^-2s^-1

9.      a) 2^nd order                     b) 6.14 x 10^-2 L mol^-1s^-1                        c) 1630 s

10.    a) rate = k[HI]²             b) 2.5 x 10²s