LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

LM 41

M.Sc. DEGREE EXAMINATION – CHEMISTRY

THIRD SEMESTER – APRIL 2007

CH 3801 – CHEMICAL KINETICS

 

 

 

Date & Time: 26/04/2007 / 9:00 – 12:00      Dept. No.                                       Max. : 100 Marks

 

 

Part A

Answer ALL the questions.                                                    (10 x 2 = 20 Marks)

1. Differentiate between time order from true order.
2. At 518 K, the half life for the decomposition of a gaseous compound initially at 363 torr

was 410 s.  When the pressure was 169 torr, the half life was 880 s.

Determine the order of the reaction.

3. The rate constant for the reaction of the type A^2- + B^– à X^3- + Y is 0.2 M^-1 min^-1 in zero ionic strength. Calculate the rate constant of the above reaction in water at 25⁰C in an ionic strength of 0.5 M.
4. What is the significance of electrostriction?
5. Write down the expression for the rate constant of a reaction between two linear molecules forming a linear transition state on the basis of ARRT.
6. What is meant by ‘turnover number’?
7. For the reaction between 2NO(g) + O₂(g) à 2 NO₂(g), the observed rate decreases with increase in temperature.
8. What is meant “capillary condensation” ?
9. Calculate the Hammett acidity function (H₀) if pK_BH⁺ for the base 4 Chloro 2 nitro

aniline (B) is –3.3 and [BH⁺]/[B] = 8 x 10^-4

10. Mention the steps involved in a chain reaction with an example.

PART – B

Answer ANY EIGHT questions                                            (8 x 5 = 40 Marks)

11. Describe the potential energy surface of the following reaction. H_AH_B + H_C <=>  H_BH_C + H_A.
12. The rate constant for the decomposition of a certain substance is 1.7 x 10^-2 dm³ mol^-1 s^-1 at 24⁰C and 2.01 x 10^-2 at 37⁰ Evaluate the activation energy of the reaction.
13. Calculate the number of collisions per s between oxygen molecules in 1 cm³ at a total pressure of 1 atm and at a temperature of 27⁰ The molecular radius oxygen is 1.46×10^-8 cm.
14. Explain the kinetics of unimolecular reactions using Lindemann’s Theory.
15. Explain the significance of volume of activation for reactions in solution phase.
16. The pre-exponential factor for a certain first order reaction is 3.98 x10¹³ s^-1 and E_a = 180 KJ mol^-1. Calculate DH^#, DS^# and DG^# for the reaction at 200⁰C (R=8.314 J K^-1 mol^-1)
17. Differentiate van’t Hoff intermediates from Arrhenius intermediates.
18. Write BET equation. Mention the terms involved.  How is it verified?
19. How is Stern-Volmer constant evaluated?
20. For the following parallel first order reaction, the percentage yields of he two products B and C are 1.2 and 98.8 respectively.  The overall half life is 21.8 y.  Calculate he rate constant for each of the two parallel paths.                                                 B

A

C

21. Outline the various steps involved in the thermal decomposition of acetaldehyde.
22. Discuss the principle of flash photolysis.

PART – C

Answer ANY FOUR questions                                              (4 x 10 = 40 Marks)

23. Compare the rate constants calculated by the ARRT and the Collision Theory for the reaction between two atoms. Explain.
24. Using double sphere model for a reaction between two ions deduce the relation connecting the rate constant and dielectric constant of the medium and explain.
25. Explain an two of the following a) Relaxation methods b) Skrabal plots  c) kinetics of explosions
    26. Explain Michaelis-Menton kinetic scheme for an enzymatic reaction. Deduce the rate law and explain
    27. Discuss the mechanisms of bimolecular surface reactions with a specific example.

Deduce the rate expression for each case.

28. In the study of the kinetics of chlorination of phenol and mono substituted phenols by t-butyl hypochlorite in aqueous alkaline medium, the following data were obtained.

 

(i) At constant [substrate]₀, and [OH^–], the plots of log[t-BuOCl] vs time were linear. (ii) At constant [t-BuOCl]₀ and [OH^–], the rate increased with increase in [substrate] with first order dependences with all phenols.  The plots of k_obs vs [phenol] were linear with zero intercepts on the ordinates.  (iii) The rate decreased with increase in [OH^–] at fixed [t-BuOCl]₀ and [phenol] for the chlorination of all phenols. The plots of k_obs vs 1/[OH^–] gave straight line passing through the origin (iv) Variation of ionic strength of the medium had negligible effect on the rates of chlorination.  (v) The decrease in the dielectric constant of the medium increased the rate.   Propose a suitable mechanism to account for the above data and explain.

 

 

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LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

LM 41

M.Sc. DEGREE EXAMINATION – CHEMISTRY

THIRD SEMESTER – APRIL 2007

CH 3801 – CHEMICAL KINETICS

Date & Time: 26/04/2007 / 9:00 – 12:00      Dept. No.                                       Max. : 100 Marks

 

 

Part A

Answer ALL the questions.                                                    (10 x 2 = 20 Marks)

1. Differentiate between time order from true order.
2. At 518 K, the half life for the decomposition of a gaseous compound initially at 363 torr

was 410 s.  When the pressure was 169 torr, the half life was 880 s.

Determine the order of the reaction.

3. The rate constant for the reaction of the type A^2- + B^– à X^3- + Y is 0.2 M^-1 min^-1 in zero ionic strength. Calculate the rate constant of the above reaction in water at 25⁰C in an ionic strength of 0.5 M.
4. What is the significance of electrostriction?
5. Write down the expression for the rate constant of a reaction between two linear molecules forming a linear transition state on the basis of ARRT.
6. What is meant by ‘turnover number’?
7. For the reaction between 2NO(g) + O₂(g) à 2 NO₂(g), the observed rate decreases with increase in temperature.
8. What is meant “capillary condensation” ?
9. Calculate the Hammett acidity function (H₀) if pK_BH⁺ for the base 4 Chloro 2 nitro

aniline (B) is –3.3 and [BH⁺]/[B] = 8 x 10^-4

10. Mention the steps involved in a chain reaction with an example.

PART – B

Answer ANY EIGHT questions                                            (8 x 5 = 40 Marks)

11. Describe the potential energy surface of the following reaction. H_AH_B + H_C <=>  H_BH_C + H_A.
12. The rate constant for the decomposition of a certain substance is 1.7 x 10^-2 dm³ mol^-1 s^-1 at 24⁰C and 2.01 x 10^-2 at 37⁰ Evaluate the activation energy of the reaction.
13. Calculate the number of collisions per s between oxygen molecules in 1 cm³ at a total pressure of 1 atm and at a temperature of 27⁰ The molecular radius oxygen is 1.46×10^-8 cm.
14. Explain the kinetics of unimolecular reactions using Lindemann’s Theory.
15. Explain the significance of volume of activation for reactions in solution phase.
16. The pre-exponential factor for a certain first order reaction is 3.98 x10¹³ s^-1 and E_a = 180 KJ mol^-1. Calculate DH^#, DS^# and DG^# for the reaction at 200⁰C (R=8.314 J K^-1 mol^-1)
17. Differentiate van’t Hoff intermediates from Arrhenius intermediates.
18. Write BET equation. Mention the terms involved.  How is it verified?
19. How is Stern-Volmer constant evaluated?
20. For the following parallel first order reaction, the percentage yields of he two products B and C are 1.2 and 98.8 respectively.  The overall half life is 21.8 y.  Calculate he rate constant for each of the two parallel paths.                                                 B

A

C

21. Outline the various steps involved in the thermal decomposition of acetaldehyde.
22. Discuss the principle of flash photolysis.

PART – C

Answer ANY FOUR questions                                              (4 x 10 = 40 Marks)

23. Compare the rate constants calculated by the ARRT and the Collision Theory for the reaction between two atoms. Explain.
24. Using double sphere model for a reaction between two ions deduce the relation connecting the rate constant and dielectric constant of the medium and explain.
25. Explain an two of the following a) Relaxation methods b) Skrabal plots  c) kinetics of explosions
    26. Explain Michaelis-Menton kinetic scheme for an enzymatic reaction. Deduce the rate law and explain
    27. Discuss the mechanisms of bimolecular surface reactions with a specific example.

Deduce the rate expression for each case.

28. In the study of the kinetics of chlorination of phenol and mono substituted phenols by t-butyl hypochlorite in aqueous alkaline medium, the following data were obtained.

 

(i) At constant [substrate]₀, and [OH^–], the plots of log[t-BuOCl] vs time were linear. (ii) At constant [t-BuOCl]₀ and [OH^–], the rate increased with increase in [substrate] with first order dependences with all phenols.  The plots of k_obs vs [phenol] were linear with zero intercepts on the ordinates.  (iii) The rate decreased with increase in [OH^–] at fixed [t-BuOCl]₀ and [phenol] for the chlorination of all phenols. The plots of k_obs vs 1/[OH^–] gave straight line passing through the origin (iv) Variation of ionic strength of the medium had negligible effect on the rates of chlorination.  (v) The decrease in the dielectric constant of the medium increased the rate.   Propose a suitable mechanism to account for the above data and explain.

 

 

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LM 53

LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

FOURTH SEMESTER – APRIL 2007

CH :4807– CHEMICAL KINETICS

 

 

 

Date & Time : 16.04.2007/9.00-12.00      Dept. No.                                                      Max. : 100 Marks

 

 

Part A

 

Answer ALL the questions.                                                    (10 x 2 = 20 Marks)

1. Explain electrostriction.
2. The rate of a reaction between X and Y^– has been investigated in aqueous solution at 300 K and the second order rate constant (k₂⁰ ) at zero ionic strength is found to be 0.681 M^-1 s^-1. When ionic strength of the medium (m) is 1.60 x 10^-3 M,  the second order rate constant (k₂) is 0.901 M^-1 s^-1.  Predict the charge on X.
3. Show that collision theory of activation is less than the energy of activation calculated using the Arrhenius equation.
4. Write down the expression for the rate constant of a reaction between two linear molecules forming a non-linear transition state on the basis of ARRT.
5. The pKa for the dissociation of phenol in water at 25⁰C is 9.85. The r value for the dissociation H₂O + X-C₆H₄OH à X-C₆H₄O^– + H₃O⁺ is 2.00. If  s^–_p values of –CH₃ is –0.31, determine pKa for the dissociation of p-methyl phenol in water at this temperature.
6. What are Skrabal plots?
7. For the reaction 2NO(g) + O₂(g) à2NO₂(g), the observed rate of the reaction decreases with increase in temperature.
8. What is the significance of “Hammett acidity functions”??
9. In a typical Stern-Volmer plot graph of F₀/F (Y-axis) versus the concentration of quencher gave a straight line with slope = 640 l/mol and the rate constant of quenching is 10¹⁰ l mol^-1 s^-1. Calculate the Stern-Volmer constant and the life time.
10. Mention any four relaxation techniques employed for the study of kinetics of fast reactions.

PART – B

 

Answer ANY EIGHT questions                                            (8 x 5 = 40 Marks)

 

11. Using the Collision theory of reaction rates, derive the expression for the Collision number between two different molecules A and B
12. Calculate the rotational partition function for CO₂ in the standard state of 10³ mol m^-3 at 25⁰  The carbon-oxygen distance is 1.16 x 10^-10 m
13. Explain the need for activation energy based upon potential energy surfaces.
14. If the rate constant at high pressures for the isomerization of cyclopropane is 2 x 10^-4 s^-1 and that at low pressures is 5.14 x 10^-6 torr^-1 s^-1, below what pressure will the isomerization be for all practical purposes a second order  reaction?
15. Discus the double-sphere model for the influence of dielectric constant on the rate of an ion-ion reaction
16. Heckt and Conrad measured the rate constant (k₂) of the reaction of methyl iodide and sodium ethoxide in ethanol as 2.45 x 10^-4 M^-1 s^-1 at 285 K.  If E_a = 85.20 kJ/mol.  Calculate DG^#, DH^# and DS^# of the reaction.   (k_B=1.37 x 10^-23 J molecule^-1)
17. How is surface area of a solid deermined using BET equation.
18. For an enzyme catalyzed reaction, K_M = 25 x 10^-3 Calculate the rate of the reaction if the limiting rate is 0.64 M s^-1 and the  the initial substrate concentration of 4.32 x 10^-6 M.
19. Represent all the possible steps in a bimolecular photophysical process. Indicate the rate expression for each step.
20. For the following parallel first order reaction,  the rate constants of the two parallel paths are 3.75 and 4.65 s^-1  Calculate the percentage yield of B and also the overall half life of the reaction.                 B

A

C

21. Discuss the principle of flash photolysis.
22. Explain Bronsted catalytic law.

 

PART – C

Answer ANY FOUR questions                                              (4 x 10 = 40 Marks)

 

23. a) How will you determine the order of a reaction using dimensionless parameters?
24. b) The volume of activation for a certain reaction is – 4 x 10^-6 m³ mol^-1 at 300 K.  Calculate the pressure required to double the rate constant if the initial pressure is 10⁵
25. a) Calculate the number of collisions per second in 1 cm³ of oxygen at  27⁰C and 101.3 kPa pressure given the molecular radius of oxygen to be 1.46 x 10^-8 cm
26. b) Explain the influence of internal pressure on the rate of a reaction between neutral molecules in solutions
27. Explain the kinetics of bimolecular surface reactions with a specific example. Derive the relevant rate law for each mechanism.
28. Explain any two of the following: a) Evaluation of kinetic parameters for an enzymatic reaction b) kinetics of chain reactions  c) van’ Hoff intermediates
    27. a) Derive an expression for relaxation time for a I order reaction.
    28. b) Outline the salient features of the kinetics of explosive reactions.
    29. For the oxidation of aresenous acid by enneamolbdomanganate (IV) in perchloric acid medium, the following data were obtained: (i) Under constant [HClO₄], the second order rate constants were fairly constant. (ii) Presence of acrylonitrile  has no effect on the rate of the reaction (iii) It was found that the graph of k_obs against [H⁺]² was found to be curved passing through origin  (iv) The rate of the reaction was found to be unaffected by the increase of the ionic strength of the medium (vi) The entropy of activation was –5 J K^-1 mol^-1.  Propose a suitable mechanism to account for the above data, write the rate expression, and explain your answer.

 

 

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