[asdfomg12]

Q1: A proposed mechanism for the reaction 2NO + O₂    2NO₂ is

step(1) NO + NO  N₂O₂ (k₁ E₁ = 82kJmol^-1)

step(2) N₂O₂  NO + NO (k₂ E₂ = 205kJmol^-1)

step(3) N₂O₂ + O₂ 2NO₂ (k₃ E₃ = 82kJmol^-1)

   (a)   Derive the rate law in terms of the rate of formation of NO₂  , that is   (d[NO₂])/dt.    [10]
   
        (b)If  k₂[N₂O₂] >> k₃[N₂O₂][O₂], show that the rate law reduces to 

d[NO₂]/dt = ((2k₁k₃)/k₂)[N)²][O₂]

                                                                                                    (c)   Show that the expression given in (b)is the results obtained by using the rate determining step approximation by deriving the rate law if we assume that steps (1) and (2) are in a rapid equilibrium and step (3) is slow.

   (d)   Using the rate law given in (b), what is the overall activation energy for this reaction? 


Q2:
If  ²³⁴Pa is the end product of the decay sequence of ²³⁸U    (actually it’s  ²⁰⁶Pb), that is:

²³⁸U  ²³⁴Th  ²³⁴Pa
where the half-life of ²³⁸U to ²³⁴Th is 4.5x10⁹yr and ²³⁴Th to ²³⁴Pa is 24.1day
 
   (a)   If we start with 1 mg of  ²³⁸U , how much ²³⁸U  will be present after 60 days? 

   (b)   How much ²³⁴Th will be present after 60 days?   

   (c)   How much ²³⁴Pa will be formed after 60 days?   

Q3:
Provided  you have sets of initial rate data for enzyme and substrate, explain using words and appropriate equations how to

   (a)   Determine the partial orders and overall order of the reaction.
   (b)   Obtain the value of the pseudo-order rate constant.   
   (c)   Obtain the effective rate constant.

Q4:
For a given reaction the following half-life and initial concentration data was collected.  Use this data to determine the reaction’s order and rate constant.   
 
 
t_1/2 / s     [A]₀ / mol dm^-3
     0.160          0.050
     0.0841         0.085

Q5:
A particular enzyme catalyzed reaction was followed and data collected as indicated below.  Using the data, determine the Michaelis constant and the maximum velocity of the reaction.

[S(had to include this text to avoid strikeout text effect)]₀ / 10^-6 mol dm^-3 values in order: 31.8, 46.4, 59.3, 118.5, 222.2
v / 10^-9 mol dm^-3 s^-1 corresponding values in order: 0.070, 0.0972, 0.1167, 0.1592, 0.1945

Q6:
(a)   The half-life for a general nth order reaction is given by the expression  t_1/2 = (2^n-1 - 1)/ k(n-1)[A]^n-1₀.  Are there any reactions for which the half-life is independent of the initial concentration?  If so, what is it and does this expression apply?

   (b)   I discussed the Mechaelis-Menten mechanism of enzyme action in class.  What are its limitations?

   (c)   What is the difference between thermodynamic and kinetic control of a reaction.

   (d)   Is it possible for the activation energy of a reaction to be negative?  Explain your conclusion and provide a molecular level explanation.

   (e)   Define the terms in and discuss the limitations of the Arrhenius equation?




 

[Borek]

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