CHEM_100_11                                                                                              2013               

Assignment #5         Due to  Jan. 30

 KINETICS (chapter 14)

1.      {14}  Indicate the order ( zero, 1st or 2nd) of the rxn  Aà B  for each of the following observations

 

a)      A plot of the inverse of the concentration [A]  versus time yields a straight line

b)      The unit of rate constant is M×s-1  

c)       The rxn has a half-life that is independent of the initial concentration, [A]0

d)     the concentration of reactant [A] fall to one-half in equal intervals of time

e)      the half-life of the  rxn gets shorter as the initial concentration is increased

f)        A plot of the ln [A]  versus time yields a straight line

g)      When the initial concentration [A] doubles, the rate doubles.

h)     When [A] is reduced by a factor of 2, the rate of the reaction is reduced by a factor of 4.

i)        Change in  [A] does not change the rate  

j)       the unit of the rate constant is M-1s-1

k)     the unit of the rate constant is s-1

l)        the rate law is described by the formula : rate=k[A]2

m)   A plot of [A] versus time yields a straight line. 

n)     The rate law is described by the formula rate=k  

 

 

 

2.      {10} The data in the table below were obtained using the initial rate method for the reaction:

2ClO2 (aq) + 2OH- (aq) à ClO3- (aq) + ClO2-(aq) + H2O (l)

 

exp. number               [ClO2], M                    [OH-], M         Initial rate, M/s

1                                  0.060                           0.030               0.0248

2                                  0.020                           0.030               0.00276

3                                  0.020                           0.090               0.00828

 

a)      {5} analyze data and deduce the differential rate law

b)     {2} calculate the value of the rate constant (with units!)

c)      {1} what is the overall order of this reaction?

d)     {2} calculate the reaction rate for [ClO2]=[OH-]= 0.01M

 

 

 

3.  {10} The first-order rate constant for the reaction of methyl chloride (CH3Cl) with water to produce methanol (CH3OH) and hydrochloric acid (HCl) is 3.32 x 10-10 s-1 at 25 oC. Calculate the rate constant at 40oC if the activation energy is 116 kJ/mol.

 

 

 

 

 

 

4. {10} Consider the first-order reaction Aà product, with k=2.95 x 10-3 s-1. What percent of A remains after 100 s?

 

 

 

 

5. {10} the reaction 2Aà B is second order with a rate constant of 52 M-1 min-1 at 25oC.

(a)   {5} Starting with [A]0 = 0.0082M, how long will it take for [A]t = 2.7 x 10-7 M?

(b)   {5} Calculate the half-life of this reaction.

 

 

 

 

 

6.   {15}  The reaction Aà 2B + C is first order. If the initial [A] =1.50 M and k=1.02 x10-3 s-1,

(a) {10} what is the value of [A] after 400 s?

(b) {5} What is the concentration of B after the 400 s? Assume that volume is constant during the rxn.

 

 

 

7.  {5} The reaction 2Aà B is first order in A with a rate constant of 1.5 x 10-2 s-1 at 100oC. How long (in seconds) will it take for A to decrease from 0.30M to 0.10 M?

 

 

 

8. {6} For the elementary process N2O5 (g) à NO2(g) + NO3(g) the activation energy , Ea, is 154kJ/mol  and overall ΔE reaction  is  136 kJ/mol.

(a). {2} Sketch the energy profile for this reaction, and label Ea and ΔE.

(b) {2} What is the activation energy for the reverse reaction?

(c)    {2} Which reaction is faster, forward or reverse?

 

 

 

 

 

9. {10} Understanding the high-temperature behavior of nitrogen oxides is essential for controlling pollution generated in automobile engines. The decomposition of NO to N2 and O2 is second order with rate constant of 0.0796 M-1s-1 at 737 0C and 0.0815 M-1s-1 at 947 0C. Calculate the activation energy for the reaction.