LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034  M.Sc. DEGREE EXAMINATION – CHEMISTRY

AD 19

THIRD SEMESTER – NOV 2006

         CH 3801 – CHEMICAL KINETICS

 

 

Date & Time : 01-11-2006/9.00-12.00         Dept. No.                                                       Max. : 100 Marks

 

 

PART – A                          (10 ´ 2 = 20 marks)

 

Answer ALL the questions.

 

1. Differentiate time order from true order.
2. The half life of C–14 is 5770 years. Starting with 100 mg of C–14, how much of
   it would remain after 17,310 years.  Also calculate the decay constant.
3. What is the effect of ionic strength on the rate constant of the following reaction
   in solution?

[Fe(CN)₆]^4– + S₂O₈^2– ®  products

4. Show that the Collision theory of activation energy is less than the energy of
   activation calculated from Arrhenius equation.
5. Write down the expression for the rate constant of a reaction between two linear
   molecules forming a linear activated complex on the basis of ARRT.
6. What are “Skrabal plots”?
7. For an enzyme catalysed reaction K_M = 25 ´ 10­^–3 M and the turnover number

is 4 ´ 10⁷ s^–1, calculate the limiting rate of the reaction if [E]₀­ = 1.6 ´ 10^–8 M.

8. Mention all the steps involved in the thermal decomposition of acetaldehyde
   following a chain reaction.
9. “Adsorption if spontaneous is generally exothermic”. Explain.
10. Explain why conventional methods cannot be used for the study of kinetics of
    very rapid reactions.

 

PART – B

Answer any EIGHT questions.                                        (8 ´ 5 = 40 marks)

 

11. The rate of a reaction of the type A + B ® products was studied in solution phase
    at 298 K with initial concentration of each reactant at 0.02 M.  From the
    following data determine the order of the reaction and calculate the rate constant.

Time (min.)                                 20                            30                 40

Conc. of ‘A’ reacted

in ‘t’  (mol’/l)                      8.76 ´ 10^-3              1.07 ´ 10^–2    1.21 ´ 10^–2

12. Derive an expression for the total number of collisions of all molecules of ‘A’
    with all molecules of ‘B’.
13. Explain the kinetics of unimolecular gaseous reaction using Lindemann’s theory.
14. For hydrolysis of sulphamic acid the rate constant is 1.16 ´ 10^–3 l mol^–1 s^–1 at
    90°C with E_a = 127.61 kJ mol^–1.  Calculate DG^±,  DH^±  and  DS^± of the reaction
    occurring in solution phase.
15. Explain the significance of potential energy surfaces with an example.
16. What is the importance of “volume of activation” in the study of kinetics of
    reactions in solution.  Explain.
17. Explain the concept of Arrhenius and Van’t Hoff type intermediates.

 

 

 

18. Show that “Bronsted–Catalytic law” is a form of LFER (Linear Free Energy
    Relation)
19. The decomposition of PH₃(g) on a tungsten filament follows first order kinetics at
    low gas pressure and zero order kinetics at very high pressure.  Explain.
20. ²²⁷Ac has a half life of 21.8 years with respect to radioactive decay. The decay
    follows two parallel paths one leading to Th–227 and the other to Fr–223.  The
    percentage yields of these two daughter nuclides are 1.2% and 98.8%
    respectively.    Calculate the rate constant in y^–1 for each of the paths.
21. How is surface area of a solid determined using “BET equation”.
22. Explain the principle of “flash photolysis”.

 

 

PART – C

Answer any FOUR questions.                                         (4 ´ 10 = 40 marks)

 

23.(a)How is order of a reaction determined using dimensionless parameters.
Explain.                                                                                                  (6)

(b)Calculate the translational partition function of CO(g) in the standard state of
1 mol/l at 27° C.                                                                                    (4)

24.(a) Explain the “single sphere model” for a reaction between two ions in

solution.                                                                                                            (5)

(b) Discuss the importance of Hammett equation with one example.       (5)

25. Explain the kinetics of bimolecular surface reactions with a specific example.

Derive the relevant rate laws in each mechanism.                               (5 + 5)

26. Discuss the kinetic scheme for a single substrate enzymatic reaction and

Explain how the kinetic parameters can be evaluated.                        (5 + 5)

27. Explain any two of the following: (5 + 5)

(a) Kinetics of reversible reactions (both I order)

(b) Determination of   k_H⁺  for an acid catalysed reaction.

(c) Expression for relaxation time for a I order reaction

(d) Stern–Volmer equation

28. (a) The decomposition of ozone 2O₃ ® 3O₂ proceeds through the mechanism

 

(i) O₃ Û O₂ + O with k₁ is the rate constant for the forward reaction and k₂ is the rate constant for the backward reaction

(ii) O₃ + O  Û 2O₂ (slow step)

Derive expression for the rate of reaction using

• equilibrium approach for step (i)
• Steady state treatment for O . (7)

(b) How is the energy of activation for the overall reaction above related to the
energies of activation for the individual steps?                                 (3)

 

 

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