chemistry Honours(H3) 3rd sem 2014 previous year BSc question paper | Assam University
TDC Odd Semester Exam., 2014
CHEMISTRY
Honours
( 3rd Semester )
Paper No. : CHMH—303
(Physical Chemistry—HI)
Full Marks: 35
Pass Marks: 12
Time: 2 hours
The figures in the margin indicate full marks for the questions
Answer five questions, taking one from each Unit
UNIT—I
1. (a) A thermodynamic engine works between ice point and steam point. It is desired to increase the efficiency by 20% (i) keeping the temperature of the source constant and (ii) keeping the temperature of the sink constant. Calculate the change in temperature in each case. 2+2=4
(b) Show that, in an irreversible process 1S >0. What is Clausius inequality?
2. (a) Derive an expression for entropy change of an ideal gas in an isothermal process.
(b) Discuss two limitations of the first law of thermodynanics. 2
(c) Calculate AS accompanying freezing of 1 mol of water at 298 K to ice at 263 K. Given that the heat of fusion of ice is 6 kJ mol, the heat capacity of ice and liquid water are 36’82 JK1 moF1 and 7531 JK’ moFt respectively. 3
UNIT—Il
3. (a) Derive thermodynamically van’t Hoff reaction isotherm. 3
(b) (1) The value of K for the water gas reaction CO +H2OCO2 + H2 is 106 x i05 at 25 °C. Calculate the standard state free energy change (AG°) of the reaction at 25 °C (R = 8.3 14 3K1 mol’).
(ii) Derive van’t Hoff equation for the temperature dependence of equilibrium constant. 2+2=4
4. (a) Integrate the van’t Hoff equilibrium and determine the constant of integration. 3
(b) Find an expression for of the following equilibrium N2(g) +3H2(g)2NH3(g) Hence state the effect of pressure on the state of equilibrium of the reaction. 3+1=4
UNIT—Ill
5. (a) Thermodynamically derive the relation between the relative lowering of vapour pressure with mole fraction of the solute in a dilute solution. 3
(b) Calculate the molecular weight of urea, when 0184 g of urea is dissolved in 100 cc of water. The solution has an osmotic pressure of 56 cm (Hg) at 30 °C. 2
(c) “Relative lowering of vapour pressure is independent of the nature of solute.” Justify. 2
6. (a) Derive thermodynamically the relation between the elevation of boiling point of a dilute solution and the molal concentration of the solute. 3
(b) Provide the difference between ideal and non-ideal solutions.(4)
(c) Find the boiling point of a solution containing O’36 g of glucose (C6H1206) dissolved in 100 g of water. (Kb =052 Kmo11). 2
UNIT—IV
7. (a) The resistance of a decimolar salt solution occupies a volume between two point electrodes 1 8 cm apart and 54 cm2 in area was found to be 32 ohms. Calculate the molar conduct ance of the solution. 2
(b) For a uni-univajent electrolyte, write Onsager equation. 1 I
(c) Describe moving boundary method for determination of transport number of an ion. 4
8. (a) Write a note on conductometric titration. What are the advantages of conductometrjc titration over conventional titration? 2+2=4
(b) Calculate pH of a solution obtained by mixing 5 g acetic acid and 75 g sodium acetate and making the volume to 500 ml. Given that Ka for acetic acid is 18x105 at 25°C. 3
UNIT—V
9. (a) Define number-average and mass- average molecular mass of macro olecules. 11/2+1 ‘/2=3
(b) Write a short note on ‘addition polymerization’.
(c) Calculate M (weight-average molecular weight) for a system containing equal number of particles with molecular weights 10000 and 20000.
10. (a) Discuss viscosity method for the determination of molecular weight of a polymer. 3
(b) In a particular sample of a polymer, 100 molecules have molecular weight each, 200 molecules have molecular weight 1O each and 200 molecules have molecular weight 10 each. Calculate the number-average molecular weight. 2
(c) Differentiate between natural and synthetic polymers. 2
J15—500/153 N-14/ODD/CHMH_303/252
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