LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

B.Sc. DEGREE EXAMINATION – CHEMISTRY

WD 09

THIRD SEMESTER – April 2009

CH 3500 – PHYSICAL CHEMISTRY – I

 

 

 

Date & Time: 06/05/2009 / 9:00 – 12:00  Dept. No.                                                   Max. : 100 Marks

 

 

 

PART – A

Answer ALL the questions                                                                 (10 x 2 = 20 marks)

 

1. Distinguish C_p and C_v of an ideal gas.
2. Define: Integral heat of dilution.
3. Deduce the relationship between K_p and K_c for the following reaction

2NO(g) + O₂(g)     2NO₂(g)

4. Dissociation of NH₄Cl is represented by the equation

2NH₄Cl(s)      NH₃(g) + HCl(g)

What is the number of components for it if a start is made with (i) pure NH₄Cl    (ii) NH₄Cl  and either product of dissociation

5. State Le Chatelier’s principle.
6. Apply phase rule to the triple point of water.
7. State Hess’s law of heat of summation.
8. Calculate the root mean square velocity of O₂ molecule at 27°C.
9. “Addition of a non-volatile solute lowers the vapour pressure of a solution” – Offer a theoretical explanation for this statement.
10. State the Nernst distribution law.

PART – B

Answer any EIGHT questions                                                            ( 8 x 5 = 40 marks)

 

11. Show that the entropy of mixing of ideal gases is positive.
12. The standard enthalpy of formation of HCl gas at 25°C is -22.06 kcalmole^-1. Calculate the ΔE of formation at 25⁰C.
13. State third law of thermodynamics. Explain how the absolute entropy of a substance can be determined on the basis of the third law of thermodynamics.
14. State and derive Gibb’s phase rule.
15. Water gas reaction is represented by the equation

C_(s) + H₂O_(g)     CO_(g) + H_2(g)

1. What is the equilibrium law expression for the reaction?
2. State, giving reasons, how this equilibrium will shift if
3. all pressures are doubled
4. the temperature is increased

 

16. Deduce gas laws on the basis of the kinetic theory of gases.
17. State and explain Henry’s law. What are the limitations of this law?

 

 

 

 

18. What is meant by critical solution temperature? How can it be determined for phenol-water system? Explain the effect of addition of NaCl on the critical solution temperature.
19. How can the molecular mass of a nonvolatile solution be determined from freezing point measurements?
20. A 0.1formal solution of NaCl is found to be isotonic with a 1.10% solution of urea. Calculate the apparent degree of dissociation of NaCl.
21. Apply phase rule to Lead-Silver system and discuss the desilverisation of lead from this system.
22. Draw and explain the phase diagram of any three component system having one partially miscible pair.

PART – C

Answer any FOUR questions                                                                         ( 4 x 10 = 40 marks)

 

23. Derive Maxwell’s equations from basic thermodynamic ralations.
24. a. Derive Gibbs-Helmholtz equation.
25. The measured heats of neutralization of acetic acid, formic acid, hydrocyanic acid and hydrogen sulphide are 13.20, 13.40, 2.90 and 3.80 kcal per geq. respectively. Arrange these acids in the decreasing order of strength.
26. Draw the phase diagram of FeCl₃-H₂O system and describe its complete labeling. Explain, What do you understand by the isothermal evaporation of the solution.
27. a. State and explain Raoult’s law.
28. What are azeotropic mixtures? Give examples.
29. a. What are abnormal colligative properties? How will you calculate the vant Hoff factor and degree of dissociation of a solute from the measurement of colligative properties?
30. 0.9g of a solute was dissolved in 100ml of benzene at 25°C when its density is 0.879g/ml. The solution boiled 0.250°C higher than the boiling point of benzene. Molal elevation boiling point constant for benzene is 2.52 Kkgmol^-1. Calculate the molecular weight of the solute.

 

28. Derive thermodynamically the relation connecting elevation in boiling point of a solution of a non-volatile solute in a volatile solvent and its molality.

 

 

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