IGNOU MSCANCHEM MCH 13 SOLVED ASSIGNMENT

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MCH 13 2025 - English

ASSIGNMENT

MCH-013: General Physical Chemistry

Course Code: MCH-013

Assignment Code: MCH-013/TMA/2025

Maximum Marks: 100

Note: Attempt all questions. The marks for each question are indicated against it.

1. Answer any five of the following in brief.

a) Give the physical significance of Helmholtz energy.

b) What is the effect of temperature on chemical potential?

c) Explain the molecular partition function in brief.

d) What is the improper rotation of the molecules? Explain with a suitable example.

c) Give the characteristics of the unimolecular reactions.

f) Define the primary and secondary salt effects on the rate of reactions in solution.

g) Why the conventional kinetic methods are not useful to study the fast reactions?

2. (a) Determine the conditions for the spontaneity and equilibrium for following combinations of AH and AS for a given process.

(i)

(ii)

(iii)

(iv)

(b) (i) Two moles of an ideal gas expand isothermally at 300 K from 7 bar to 3 bar. Calculate the change in the Helmholtz energy and Gibbs energy for the process.

(ii) Define partial molar volume and give its physical significance.

3. (a) Give Stirling's approximation and outline its significance. Calculate the % error introduced in computing the value of 10! by using this approximation. (Given In 2=0.69 and In 3= 1.01)

(b) (i) A system consist of two energy level 60 and 61 which are singly and triple degenerate, respectively. Calculate the partition function of the system.

or

Derive the relation between molecular and canonical partition function.

(ii) Derive an expression for the rotational partition function.

4. (i) Define Tetrahedral and Octahedral voids in three dimensional close packing.

ii) If atoms of element B form HCP lattice and 2/3rd of tetrahedral voids are occupied by those of the element A, what is the formula of the compound formed by the elements A and B?

(iii) State the law of constancy of interfacial angles.

(b) (i) Show the following planes in cubic unit cells

i) (110) in Primitive cubic cell

ii) (111) in Face-centred cubic cell and

iii) (200) in Body-centred cubic cell.

(ii) Give the difference between screw Axis and glide Plane by using suitable illustrations.

or

Identify all the symmetry elements in trans C₂H₂Cl₂or B₂Cl₆

5. (a) Give the salient features ofthe collision theory and calculate the factor that relates the collision theory with Arrhenius Equation.

b) (i) Discuss the Lindemann-Christiansen mechanism for unimolecular reactions and give the Hinshelwood's modification of this mechanism.

(ii) What are two important features of the expression for rate of activation as per RRK theory?

6. Answer any five of the following in brief.

a) Give the principle of ultrasonic relaxation methods for the determination of the rates of the fast reactions.

b) Explain the difference between homogeneous and heterogeneous catalysis with suitable examples.

c) Describethe lock and key hypothesis of the enzyme action.

d) What is the role of solvent in the Debye-Huckel model of a solution of an electrolyte?

e) Why did we need the modification in the Debye-Huckel theory?

f) Give the mathematical expressions of any two type of Maxwell and Boltzmann distribution of molecular speeds and name the terms involved.

7. g) What is the effect of pressure and temperature on thermal conductivity?

(a) Derive the expression of the rate constant for reactions in solution in terms of activity where the reference standard state for the reactants is the gaseous state.

(b) (i) What is the difference between diffusion controlled and activation-controlled reactions.

(ii) Discuss the stopped flow method for the study of fast-reactions with suitable schematic diagram and outline its advantages over continuous flow method.

8. (a) What is adsorption in homogeneous catalysis? Derive an expression for Langmuir monolayer adsorption isotherms for adsorption at sufficiently low concentrations.

(b) (i) What is the difference between competitive and uncompetitive enzyme inhibition?

(ii) Derive the mathematical rate expression for competitive enzyme inhibition and give the graphical representation of Lineweaver-Burk plot.

9. (a) (i) Write the basic assumptions of the Debye-Huckel theory.

(ii) Calculate the ionic strength of

i) 0.08 mol kg¹ solutions of Ca(NO3)2 and

ii) the solution consisting of 6.3 g of MgCl2, 5 g of AlCl3 and 500 g of water.

(b) (i) List different methods of experimental determination of activity coefficients.

(ii) Explain the principle for the experimental determination of activity and activity coefficient from solubility measurements.

10. (i) What are the limitations of phenomenological approach to transport properties?

(ii) Using the Fick's first law of diffusion, derive the mathematical expression that provides the link between the phenomenological and thermodynamic treatment of diffusion phenomenon.

b) (i) Why is conductivity not a suitable quantity to compare the conduction behaviour of different electrolytic solutions?

(ii) Define thermal conductivity. Why the thermal conductivity of gases is independent of pressure up to a reasonably high pressure.

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