Possibly Useful Physical Constants







Possibly Useful Equations

For ;       where n is the order of the reaction.

The Arhenius equation:    

For a fast equilibrium between and ; Relaxation time

Unimolecular gas phase reaction ; and          

Bimolecular gas phase reaction ; and

For           ;        
                                       k1                                                     k2
For   E      +    S   ES           P ;          and    
                                     k–1
Fluorescence lifetime   ;        



1.
A second order reaction of the type
                              2A Product,
is 40.0 % complete in 120 minutes when the initial concentration of A is 0.02 M. What is the time required for the reaction to be 40.0 % complete when the initial concentration of A is 0.1 M?
A.
24     min
B.
60     min
C.
240   min
D.
36     min
E.
48     min


2.
For a first order reaction
A     products
the concentration of A changes from 0.1M to 0.025 M in 40 minutes. The rate of reaction when the concentration of A is 0.01 M is:
A.
3.47 × 10–4   M / min
B.
1.73 × 10–5   M / min
C.
3.47 × 10–5   M / min
D.
1.73 × 10–4   M / min
E.
2.73 × 10–4   M / min


3.
Which of the following choices for the one-step hydrolysis of an organic chloride in presence of a large excess of water,
RCl + H2O ROH + HCl    
is correct?
 
     Molecularity      Order    
A.
        2                            1
B.
        2                            2
C.
        1                            2
D.
        1                            1
E.
        2                            0


4.
The concentration of A in the reaction A P was measured as a function of time and the following data are obtained
[A]/(M)
1.0
0.75
0.40
0.10
t    /(min)
0.0
0.05
0.12
0.18

The order of the reaction is
A.
0
B.
1
C.
2
D.
3/2
E.
cannot be determined


5.
The age of a cloth is determined by dating. A sample of an ancient cotton cloth undergoes 13.0 decays per minute while a sample of fresh cotton of the same mass undergoes 15.4 decays per minute. Given that the half-life of is 5760 years calculate the age of the cloth in years.
A.
1408
B.
C.
5760
D.
3300
E.
2900


6.
Which of the following statements is not correct.
A.
The reaction path is not affected by a catalyst.
B.
The catalyst modifies the reaction path.
C.
A reaction progresses from reactants to products along a minimum energy path.
D.
The activated complex () can change to either products or reactants.
E.
The activated complex theory assumes an equilibrium between reactants (and ) and activated complex ().


7.
A linear least squares fit of for a gas phase second order reaction gave the following equation,
for this reaction at is:
A.
B.
C.
D.
E.


8.
Assuming that the decomposition of into products involves the formation of an excited molecule ,
                           
which is short-lived and may be deactivated by collision with an molecule,
                       
or decompose into products,
                                     
apply the steady state approximation to arrive at the expression for the decomposition rate .
A.
B.
C.
D.
E.


9.
On irradiating a solution of Anthracene () with ultraviolet light of intensity it dimerizes,
22
and a 'photostationary' state (at which [] is constant) is reached. A reasonable mechanism for this process is:
               
               
               
               
Apply the steady state approximation on and to show that the general expression for is:
A.
B.
C.
D.
E.


10.
Under certain condition the rate of reaction:
H3PO4 (aq) + 3I–(aq) + 2H+(aq) H3PO3(aq) + I3–(aq) + H2O(l)

is given by,
R = k [H3PO4][ I–][ H+]2.

Which of the following actions would double reaction rate?
A.
Doubling [I–].
B.
Halving [H+].
C.
Increasing [H3PO4] four times and halving [H+] and [I–].
D.
Doubling [I–] and halving [H+].
E.
Doubling [I–] and halving [H3PO4].


11.
Consider the reaction,
 

The activation energy of the forward reaction is. What is the activation energy of the reverse reaction
 
A.
+
B.
C.
+
D.
+
E.
+


12.
The relaxation time τ for the reaction
k1
A   P
k–1

is . If k1 is 1250 , then k–1 is:
A.
1780 s–1
B.
1250 s–1
C.
830 s–1
D.
2134 s–1
E.
500 s–1


13.
Consider the following parallel reactions;
                      k1
          CH4     →   CH2 + H2

                         k2
              CH4     →   CH3 + H
                           
a plot of versus time (t) yields a slope of –3.88×1012 s–1. If then k1 in is
     
A.
1.31×1012
B.
7.63×1010
C.
1.31×1014
D.
1.43×109
E.
1.34×107


14.
Data for a first-order reaction indicate that its half-life is 10.0 min at 700 K and 260 min at 600 K. The activation energy for this reaction is:
A.
114  
B.
87    
C.
70    
D.
26    
E.
145  


15.
For the sequential reaction;

where kA and kB are 5.0 ×106 s–1 and 3.0 ×106 s–1. The time at which [B] is at its maximum value is:
A.
2.6×10–7 s
B.
1.3×10–4 s
C.
7.2 ×10–6 s
D.
3.4 ×10–5 s
E.
4.8 ×10–7 s


16.
Which of the following occurs when the reaction,
k1
S       P
k–1
is catalyzed?


                                     
A.
increases     increases      unchanged
B.
decreases    increases      decreases
C.
increases     decreases      increases
D.
increases     decreases      unchanged
E.
decreases    decreases      unchanged


17.
Determine the Michaelis constant from the initial rates at initial substrate concentrations given in the following table and a maximum rate for an enzyme-catalyzed reaction proceeding by the mechanism,
                                                             k1
                         E      +    S       ES           P
                                                             k–1
   
 
2.5
 
4.0
 
10
 
28
 
40
 
70

A.
B.
C.
D.
E.


18.
The following mechanism has been proposed for the hydrolysis of in a basic medium.




Assuming that andare in a steady state derive the expression for the rate of this reaction.
A.
B.
C.
D.
E.


19.
Fluorescence at 310 nm is used to measure the amount of hydrolysis of a certain substance. The fluorescence intensity is found to be a linear function of concentration. If the intensity of a 1.2 of a standard is 80, and the intensity of an unknown is two-thirds the intensity of the standard, then the concentration of the unknown in is:
A.
0.8
B.
0.5
C.
1.2
D.
40
E.
53


20.
The fluorescence lifetimes () of de-excited propanone varied with the concentration of quencher [Q] according to the relation

indicating that the contributions of internal conversion () and intersystem crossing () are negligible. Which of the following choices for το, the fluorescence lifetime in the absence of a quencher, and kq, the rate constant for collisional quenching, is correct?


                   
                                                                 
A.
                 
B.
                   
C.
                 
D.
             
E.
             


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