LOYOLA COLLEGE (AUTONOMOUS), CHENNAI –600 034

B.Sc., DEGREE EXAMINATION – CHEMISTRY

FIFTH SEMESTER – NOVEMBER 2003

CH – 5500/CHE508 –  PHYSICAL CHEMISRTY – II

03-11-2003                                                                                                     Max:100 marks

1.00 – 4.00

 

PART – A                                           (10X2=20 marks)

Answer ALL questions.

 

1. Write the electrode reaction occurring in a saturated calomel electrode when it serves as cathode.
2. NaCl cannot be used in salt bridge preparation. Why?
3. Calculate E_cell for Cu | Cu²⁺ (10^-2‑M) || Ag⁺ (10^-3M)| Ag at 298 K. E^o red for Cu²⁺ | Cu is 0.34V, Ag⁺ | Ag 0.8V.
4. Write the electrode reactions occurring in a lead storage battery when it serves as a source of current.
5. Define molar conductance of an electrolytic solution.
6. 30% of a zero order reaction is complete in 100 min. Calculate i) rate constant ii) half life.
7. Mention the steps involved in a thermal chain reaction with one example.
8. Predict the effect of ionic strength on the rate constant of the following reaction and account for your answer.

S₂O₈^2- + 2I^–    2SO₄^2- + I₂

9. Adsorption if spontaneous must be exothermic.
10. Why is quantum yield for H₂ + Cl₂   2 HCl very high?

 

PART – B                                           (8X5=40 marks)

Answer any EIGHT questions.

 

11. Explain the construction and working of Weston saturated standard cell. Write the electrode reactions involved.
12. E^o cell for Pt | H₂ HCl (aq) | H_gCl­₂(s) | H_g­ is 0.2699V at 293 K and 0.2669 V at 303 K. Evaluate the thermodynamic parameters DG^o, DH^o and DS^o at 298 K.  (Assume two electron transfer)
13. How is pH of a solution determined using quinhdrone electrode?
14. E^o red for Ag-AgCl electrode is 0.22V and for Ag⁺ | Ag is 0.8 V at 298 K. Calculate the solubility product of AgCl and the solubility of it in water in g/l.  (Molecular mass of AgCl : 143.5).
15. How is K_a of a weak acid determined experimentally using conductance measurements?
16. For a reaction with an activation energy of 50 kJ/mol the temperature is increased from 25^oC to 37^o Calculate the ratio of the rate constants (R = 8.314 JK^-1 mol^-1).
17. The following mechanism is proposed for the decomposition of ozone in the atmosphere.
18. k­₁

0₃            O₂ + O

k₂

1. ii) O + O₃ k₃ O₂ + O₂    (slow step)

 

Derive an expression for the rate of decomposition of O₃ using steady state

approximation with O treated as the intermediate.  Show that when the second step is

slow, the rate is second order in O₃ and  first order in  O₂.

18. The pre-exponential factor for a bimolecular gaseous reaction at 300^oC is 7.4 X 10¹⁰ l mol^-1 s^-1. Calculate DS^¹.
19. Differentiate physisorption form Chemisorption (five points).
20. Explain a) Photosensitization b) Parallel reaction with one example for each.
21. The quantum yield is 2 for the photolysis of HI(g) to H₂ + I₂ by light of wavelength 253.7 nm. Calculate the number of moles of HI that will be decomposed if 300 J of energy of this wavelength is absorbed.
22. Explain Langumir – Hinshelwood mechanism with one example.

 

PART – C                                           (4X10=40 marks)

Answer any FOUR questions.

 

23. a) Derive Nernst equation for a cell reaction and hence deduce an expression relating equilibrium constant and E^o         (4+2)
24. b) Explain the significance of electromotive series. (4)
25. Derive an expression for E cell for a concentration cell with transference and hence deduce an expression for liquid junction potential.          (7+3)
26. a) Explain the principle of polarography. (5)
27. b) How is transport number of an ion determined experimentally? (5)
28. a) Account for the variation of equivalent conductance with concentration for i) strong electrolyte ii) weak electrolyte. (5)
29. b) Derive an expression for rate constant of a second order reaction of the type 2A                                                                                                       (5)
30. a) Explain any two methods of determining order of a reaction. (4)
31. b) Derive Langumir adsorption isotherm equation and apply it to a moderately adsorbed system.         (5+1)
32. a) Compare collision theory with ARRT (5)
33. b) Explain the principle of flash photolysis. (5)
34. Explain the kinetics of enzyme catalysed reaction involving a single substrate. How are the kinetic parameters for the enzymatic reaction evaluated?                                         (10)

 

 

 

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