THIRD SEMESTER – NOVEMBER 2003

CH – 3500/CHE504 – PHYSICAL CHEMISRTY – I

04-11-2003 Max:100 marks

9.00 – 12.00

PART – A (10X2=20 marks)

Answer ALL questions.

Define Molar heat capacity at constant volume.
State the third law of thermodynamics.
Heat supplied to a Cornot engine is 1897.86 kJ. How much useful work can be done by the engine which works between 0^oC and 100^oC?
Mention the criteria of reversibility interms of S and G.
For the reaction C(graphite) + 1/2 O₂ (g) CO (g) at 298k and at 1 atm pressure, DH = 110.60 kJ. Calculate D
Define Ebullioscopic constant of a liquid?
What are isotonic solutions? Give an example.
Mention the importance of critical Solution Temperature.
Express the conditions for the validity of the distribution law.
Determine the number of degrees of freedom for the following equilibrium at 1 atm premure.

Water (liquid) water (vapour).

PART – B (8X5=40 marks)

Answer EIGHT questions.

Show that for an ideal gas
a) (= 0. b) ( = 0.
Internal energy and enthalpy remain constant in the isothermal expansion of an ideal gas – Explain.
For the reaction N₂ (g) + 3H₂ (g) 2 NH₃(g). K_p is 1.64 x 10^-4 at 673 k. Calculate DG when the partial pressure of N₂, H₂ and NH₃ are 10 atm, 30 atm and 3 atm respectively. Is the reaction spontaneous?
Discuss the effect of temperature on enthalpy change of a reaction.
Obtain an expression for the equilibrium constant thermodynamically.
Explain with an example the positive deviation from Raoult’s law.
How will you determine the molecular weight by Beckmann’s method.
Highlight the salient features of the phase diagram of water system.
Derive thermodynamically the distribution law.
Draw and explain the phase diagram of a system having both UCST and LCST.
An immisible mixture of water and quinoline boils at 98.9^oC under a pressure of 740 torr. The distillate contains 77.9 g of quinoline and 1 kg of water. At the given boiling point the vapour pressure of quinoline is 7.96 torr. Calculate the molar mass of quinoline?
Derive any two Maxwell’s relationships.

PART – C (4X10=40 marks)

Answer FOUR questions.

Obtain expressions for w, Du and DH for the reversible isothermal expansion of real gas.
a) How is Joule-Thomson coefficient calculated? Mention the importance of inversion

temperature. (7)

b) Calculate the ratio of K_p to K_c at 27^oC for the following equilibrium. (R = 0.082 lit

atm K^-1 mol^-1)

COCl₂ (g) CO_(g) + Cl₂(g). (3)

a) Discuss the application of Lechatelier’s principle to the formation of ammonia. (6)
b) Two moles of an ideal gas undergo isothermal reversible expansion from 15 litres to 30

litres at 300 K. Calculate the work done and change in entropy. (4)

a) Draw the vapour pressure – composition and boiling point – composition curves of

completely miscible binary solutions. (5)

b) Explain the principle of steam distillation. (5)
Derive phase rule equation and explain the terms involved in it with one example.
a) How will you determine osmotic pressure of a solution by Berkely – Hartley method? (5)
b) A 0.5% aqueous solution of kCl was found to freeze at -0.24^o Calculate the van’t

Hoff factor and the degree of dissociation of the solute at this concentration (k_f = 1.86 K

kg mol^-1). (5)

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