CHEMISTRY (Physics Chemistry)

Optional Paper—1

Time : 3 Hours

Maximum Marks : 50

N.B. :— (1) All questions are compulsory and carry equal marks.

(2) Draw well labelled diagram wherever necessary.

1. (A) Derive the relationship between heat of reaction at constant volume and constant pressure. The

heat of combustion of benzene in a bomb calorimeter was found to be –3263.9 kJ mol^{–1} at

298 K. Calculate the heat of combustion of benzene at constant pressure. [5M]

(B) Define :

(i) Isobaric process

(ii) Isochoric process

(iii) Adiabatic process

(iv) Reversible process, and

(v) Cyclic process. [5M]

**OR**

(C) State Joule-Thomson effect. Show that Joule-Thomson effect is isoenthalpic. [2½M]

(D) Calculate maximum work-done when 3-moles of nitrogen gas expands isothermally and reversibly

from volume of 5 dm3 to 20 dm3 at 30ºC. [2½M]

(E) Explain with suitable example Hess’s Law of constant heat summation. [2½M]

(F) State and explain state function and path function. [2½M]

2. (A) Discuss water system with the help of phase diagram. [5M]

(B) State and explain Nernst distribution law. Find out amount of solute extracted from 100 ml of

an aqueous solution containing 9 gm of it using 50 ml CHCl_{3} at a time in two instalments. The

distribution coefficient of solute between CHCl_{3} and water is 5. [5M]

**OR**

(C) Define :

(i) No. of components and

(ii) Degrees of freedom. [2½M]

(D) Draw phase diagram of Lead-Silver System and explain the principle of Pattinson’s process for

enrichment of Silver. [2½M]

(E) What is critical solution temperature ? Explain nicotine-water system. [2½M]

(F) State and explain the Raoult’s Law of an ideal solution. [2½M]

3. (A) State and explain Kohlrausch’s Law of ionic mobility. At 25ºC l¥ for potassium picrate is

103.97 × 10^{– 4} Sm^{2} mol^{–1} and l¥ of potassium ion is 73.58 × 10^{–4} Sm2 mol^{–1} . Calculate l¥ for

picrate ion and transport number of picrate ion at infinite dilution. [5M]

(B) Explain :

(i) Relaxation effect and

(ii) Electrophoretic effect. [5M]

**OR**

(C) Explain Arrhenius theory of electrolytic dissociation. [2½M]

(D) A 0.5 N solution of a salt has the resistance of 25 ohms. Calculate the specific conductance and

equivalent conductance of the solution. (Given : Cell constant = 38.22 m^{–1}). [2½M]

(E) Explain conductometric titration of strong acid against strong base. [2½M]

(F) What is transport number ? Derive the relation between ionic conductance and transport number

of an ion. [2½M]

4. (A) Define activation energy of a chemical reaction. How can it be determined with the help of

Arrhenius equation ? In the reaction of decomposition of acetaldehyde the slope of straight line

for a plot of log K against

T

1

is found to be –9920 K. Calculate the energy of activation. [5M]

(B) Discuss transition state theory. Derive an expression for the rate constant based on equilibrium

constant. [5M]

**OR**

(C) Distinguish between order and molecularity of a reaction. [2½M]

(D) In a gaseous reaction the time for half change for various partial pressures was as follows :

Pressure (mm) : 200 300 400

Half time (min.) : 150 99.8 75.3

What is the order of reaction ? 2½

(E) Derive an expression for the rate constant for reaction of second order when initial concentrations

of both reactants are equal. [2½M]

(F) Discuss the Lindemann’s theory as applied to the unimolecular reaction. [2½M]

5. Attempt any TEN questions out of the following :

(i) What are extensive properties ?

(ii) What is inversion temperature ?

(iii) Give two statements of first law of thermodynamics.

(iv) What is triple point of a system ?

(v) Write condensed phase rule equation.

(vi) What are azeotropic mixtures ?

(vii) What is cell constant of a conductivity cell ?

(viii) Write two advantages of conductometric titrations over usual titrations.

(ix) Write Debye-Huckel-Onsager equation.

(x) What is zero order reaction ? Give one example.

(xi) What do you know about stearic factor ?

(xii) Write unit of rate constant of first order reaction. [10M]

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