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Indira Gandhi National Open University (IGNOU) 2005 B.Sc Chemistry Physical - - Question Paper

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CHE-4

BACHELOR OF SCIENCE (B.Sc ) Term-End Examination June, 2005

CHEMISTRY CHE-4 : PHYSICAL CHEMISTRY

Maximum Marks : 50

Time: 2 hours

JVofe ;

(i) Attemp* all the parts* Answer five questions from each of the three parts_s A, B and G From Part D, ansiuer four questions.

Logarithmic fab/es may be obtained from the Hall Superintendent for .use*

PART A

Answer any five questions.

1. Write down the following with proper SI unit symbols and prefixes :

(a) 10"⁹ metre

1

2. State the value of Cj C_y for helium gas. 1

3, What happens when hydrogen gas is allowed to undergo Joule-Thomson expansion at room temperature ? 1

4* Identity the type of system in each of the following cases :

(a) A tree in a garden

(b) Tea in thermos flask 1 5. What is a gel ? 1

6- Based on energy released during adsorption, how can you distinguish between physisorption and chemisorption ? 1

7. How are and /f_ related to each other for a reaction

p ^<-

between idea) gases ? 1

8, State the name given to the equilibrium point among ice, water and vapour. 1

K

9* Starting from 0 = -~, derive the relation,

^1+kp

0

^{p K(\ 9)' 2}

10- What is Tyndall effect ? Suggest an application for this effect, 2

11. State Henrys law. Why cannot fish live in warm water ? 2

12* State distribution law. State any one application of

distribution law. 2

13. Calculate the osmotic pressure of an aqueous solution containing 50*0 kg of sucrose in 1*00 m³ of a solution at 300 K (Molar mass of sucrose = 0*3.42 kg mor¹;

R = 8 314 J mor1 K"1) 2

14. Consider the following reaction,

PC1₅ <g) PC1₃ (g) + Cl₂ (3).

How would the equilibrium be affected by

(i) the addition of Cl₂ (3), and

(ii) the decrease in the volume of the container ? 2

17. The standard enthalpy of formation of H₂0 (I) at 298 K is 285-8 kJ mol^-1. Calculate the standard internal energy change [A_r ift (H₂0)) for the formation of water at 298 K. {R - 8 314 J moP¹ FT¹). 3

18. Prove that for a reversible adiabatic process,

T = constant, 3

19. {a) State Troutons rule.

(b) The molar enthalpy of vaporization and boiling point of ammonia are 23-3 kJ mol^-1 and 240 K respectively. Does it obey Trouton's rule ? 3

20. Derive the SI units for van der Waals constants V and b\ 3

21. Calculate the ratio u_mp : u : u_rms for a gas of molar mass M_m. Does the value of this ratio depend on temperafure ? 3

22. (a) Define quantum efficiency of a photochemical

reaction.

(b) The quantum yield for the photochemical formation of hydrogen chloride is high in the absence of oxygen but low when bxygen is present. Explain. 3

(b) Concentrated sulphuric acid contains 98% acid by weight. Its density is 1-85 x 10³ kg m^-3 Calculate its molarity.

{Molar mass of sulphuric acid = 0-098 kg mol^-1) 3

24* An aqueous solution prepared by dissolving 0*5 kg of potassium chloride in 100 kg of water was found to freeze at 272-76 K. Calculate the vant Hoff factor and degree of dissociation of solute at this concentration. K for HgO is 1-85 K kg mol^-1 and freezing point of water is 273 K. (Molar mass of KC1 is 7 45 x 10"² kg mol"¹) 3

Derive the integrated rate law for zeroth order reaction. 2

The decomposition of hydrogen iodide on gold at 323 K is zeroth order reaction and the rate constant is 1-20 x lO"⁴ M s^_1.

(b)

(i) If the initial concentration of hydrogen iodide is

0-50 M, calculate its concentration after 3 00 X io³ s.

(ii) How long will it take for all the hydrogen iodide

to decompose ? 3

Define solubility product. Explain its use in qualitative mixture analysis. 3

26. (a)

(b)

27. (a) (b)

Calculate the molarity of HCN solution that is 0*01% ionised at equilibrium. (K_a for HCN - 6*0 x 10^-1) 2

State the Faraday's laws of electrolysis. 3

1 dm³ of 2 0 M CuS0₄ solution is electrolysed using platinum electrodes by passing 4-50 A current for 9000 s. Calculate the mass of copper deposited. (Atomic mass of Cu = 63*54) 2

Derive an expression useful in calculating entropy of mixing of two ideal gases.

(b)

29* {a)

(b)

30. (a)

(b)

28, (a) State second law of thermodynamics, 2

Distinguish between 'spontaneous and non-spontaneous processes.

Starting from G = H TS_y derive the following relation ;

HG/T)

T²

dT

How do we define anode and cathode in terms of oxidation and reduction reactions ? What sign, positive or negative, would you assign to anode and cathode in (i) a galvanic cell, (ii) an electrolytic cell ? 3

Write the reactions that take place at the cathode and the anode during the discharge of a lead storage battery. 2

CHE-4 8