LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

GH 44

FOURTH SEMESTER – APRIL 2008

CH 4807 – CHEMICAL KINETICS

 

 

 

Date : 16/04/2008            Dept. No.                                        Max. : 100 Marks

Time : 9:00 – 12:00

 

PART A

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

1. Explain electrostriction.
2. Predict the influence of dielectric constant on the rate of the following reaction and estimate the sign of DS^#: [Co(NH₃)₅Cl]²⁺ + OH^– à [Co(NH₃)₅OH]²⁺ + Cl^–
3. For a reaction when the initial concentration of the reactant was 0.0135 M, the half life was 267.2 seconds and when the initial concentration was 0.054 M, the half life was 133.4 seconds. Determine the order of the reaction.
4. Write down the expression for the rate constant of a reaction between two non 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  the values of
   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 protolytic mechanisms?
7. What is turn over number in enzyme catalysis?
8. Mention the significance of Stern-Volmer coefficient.
9. Adsorption if spontaneous is mostly exothermic. Explain.
10. What is the principle of pulsed radiolysis?

 

PART – B

 

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

 

11. Show that Hammett equation is a linear free energy relation
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. The pre-expotential terms for a bimolecular gas reaction occurring at 300⁰C is 8.6 x 10¹¹ dm³ mol^-1 s^-1. Calculate the entropy of activation.  If the standard state is expressed in one molecule cm^-3, what will be the value of entropy of activation?
15. If the rate constant at high pressures for the isomerization of cyclopropane is 2 ´ 10^-4 s^-1 and that at low pressures is 5.14 ´ 10^-6 torr^-1 s^-1, below what pressure will the isomerization be for all practical purposes a second order reaction?
16. Discuss the influence of ionic strength on the rate of an ion-ion reaction in solution .
17. Explain the concept of Arrhenius and van’t Hoff type intermediates.
18. Ac-227 undergoes β-emission (98.6%) and a-emission (1.4%) in two parallel paths with an overall half-life of 21.6 years. Calculate the half life of each path.
19. Explain Bronsted-Catalytic law
20. Write BET equation and explain how surface area of a solid can be determined using the equation.
21. Derive an expression for relaxation time for a I order reaction of the type A        B
22. Explain the principle of flash photolysis.

PART – C

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

 

23. The following reaction was carried out by taking excess benzoyl chloride,

C₆H₅COCl + 2 C₆H₅NH₂ ® C₆H₅CO NHC₆H₅ + C₆H₅NH₂HCl

From the data, establish the orders in both reagents and calculate the value of rate constant.  When the concentration of benzoyl chloride was 0.015 mol dm^-3, the pseudo first order rate constant was   0.1356 min^-1

[C₆H₅COCl] = a =0.01 M;  [C₆H₅NH₂] = b = 0.0005 M

 

Time/min                                 0          5          10        15        20

10⁴ [acetanilide] /mol dm^-3      0          1.038   1.488   1.856   2.090

 

24. 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 (5)
25. b) Explain the influence of internal pressure on the rate of a reaction between neutral molecules in solution.                                                                                           (5)
26. Explain the kinetics of single substrate enzymatic reaction. How are the kinetic parameters evaluated?
27. With special reference to the reaction on a solid surface, 2CO(g) + O₂(g),® 2 CO₂(g) explain the mechanisms. Deduce the rate law in each case.
    27. Explain any TWO of the following: (5+5)
    28. a) Hammett acidity function b)Kinetics of explosive reactions
    29. c) Kinetics of consecutive reactions d)Skrabal plots

For the chlorination of phenols by t-butyl hypochlorite in aqueous alkaline medium, the following data were obtained: 1) At constant [Substrate] and [OH^–], plots of log [t-BuOCl] vs time were linear. 2) The order with respect to [Substrate] is one and the plots of k_obs vs [phenols] were linear with zero intercepts on the ordinates .  3) The rate showed inverse first order kinetics in [OH^–]. The plots of k_obs vs 1/ [OH^–] gave straight lines passing through the origin. 4) Variation of ionic strength of the medium has negligible effect on the rates of chlorination 5) Decrease in dielectric constant of the medium increased the rate.  6) ∆S^# is negative.  Propose a suitable mechanism and derive the rate law to account for the above kinetic data.

 

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LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

M.Sc. DEGREE EXAMINATION – CHEMISTRY

GH 57

THIRD SEMESTER – APRIL 2008

CH 3801 – CHEMICAL KINETICS

 

 

 

Date : 28-04-08                  Dept. No.                                        Max. : 100 Marks

Time : 1:00 – 4:00

 

PART – A

Answer All the questions:                                                                 (10×2=20)

 

1. Define time order. How is it different from true order?
2. For a reaction of the type A + B ®  products on doubling the concentration of ‘A’ alone, rate is doubled. On doubling both A and B, rate increases eight times. Deduce the total order of the reaction.
3. What is the effect of ionic strength on the rate constant of the reaction in solution?

1. Write down the expression for the rate constant of a reaction between two linear molecules forming a non-linear activated complex on the basis of ARRT.
2. What is electrostriction?
3. Define Stern-Volmer constant.
4. Mention any four relaxation techniques used for the study of kinetics of fast reactions.
5. What is capillary condensation?
6. What are van’t  Hoff intermediates?
7. Mention the significance of Hammett acidity function.

 

PART – B

Answer any EIGHT questions:                                                        (8×5=40)

 

1.  Explain the need for “potential energy surface”.
2. How is order of a reaction determined using dimensionless parameters?
3. The rate constant for the second order neutralisation of 2-nitropropane (A) by     base (B) in aqueous solution is given by the expression

 

log₁₀k  = –

The time is in minutes while the concentrations are in mol/lit. Calculate the energy of activation in cal/mol and the half life penod at 10°C when the initial concentration of each reactant is 0.008M.

1.  The rate constant of a second order gas phase reaction is 8.1 ´10⁴ M^-1 s^-1 at 331°C with  Calculate for the reaction.
2. How is volume of activation for a reaction in solution determined experimentally? Mention its significance.
3. Outline the importance of Hammett linear free energy relation.
4. Explain Skrabal plots.
5. How is surface area of a solid determined using multilayer adsorption studies.
6. For the weak base 2- nitro anilene (B) in 0.02M HClO₄ the ratio of (BH⁺) to (B) is 0.01. Calculate

1. i) _pk_BH⁺ for 2-nitro anilinium ion and
2. ii) the ratio of (BH⁺) to (B) in 0.05M HClO₄ using the same indicator.

 

1. Derive an expression for relaxation time for a I order reaction.
2. Explain Bronsted- catalytic law.
3. Write down all the steps involved in the thermal decomposition of acetaldehyde with the relevant rate expression for each step of the chain reaction.

 

PART – C

Answer any FOUR  questions:                                                        (4×10=40)

 

1. Explain the kinetics of unimolecular gas phase reactions with relevant derivations.
2. Explain the double sphere model for the influence of dielectric constant on the rate of an ion-ion reaction in solution.
3. In the Kinetic study of the Oxidation of N-ethyl anilene(S) by peroxomono sulphuric acid (O) the following results were obtained.

1. The reaction follows I order kinetics with respect to each
2. The rate decreases with decreasing [H⁺]

• Addition of LiClO₄ (aq) has no effect on the rate

1. is found to be negative.

Interpret these observations and suggest a suitable mechanism with the rate expression.

1. Discuss the kinetics of bimolecular surface reactions with the relevant mechanisms and rate laws.
2. Explain any two of the following

1. Stern – Volmer equation
2. Hammett acidity function
3. Flash photolysis
4. Evaluation of k_H⁺ for a specific hydrogen ion catalysis.

1. a) Derive an expression for rate constant of a I order parallel reaction and explain

1. b) Explain the mechanism of single substrate enzymatic reaction.

 

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