Q7/15Q/11-12 Reg. No

St. Joseph’s College of Arts& Science (Autonomous) St. Joseph’s College Road, Cuddalore – 607001 PCH703 – PHYSICAL CHEMISTRY - I Time : 3 hrs Max Marks : 75

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SECTION - A (20X1=20) Answer ALL Questions I. Choose the correct answer:1.

For a given reversible reaction. E a forward is 80 KJ & E a backward is 100 K J and its heat of reaction is a) 20 KJ (endothermic) b) 20 K J (exothermic) c) -20 KJ (endothermic) d) -20 KJ (exothermic) R

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The change in chemical potential for 56 g of oxygen allowed to get compressed from 10 atm to 5 atm pressure at 25°C is a) 34.7 b) 413.1 c)17.3 d) 206.6

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The product of A 1g x B 1g of D 6h is a) A 1g b) B 1g R

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c) A 1u R

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d) B 1u R

For electrophilic aromatic substitution, the proposed mechanism is + + + ( ArHE ) ArH + E ArE + H fast (slow) It is therefore expected that k H /k D . a) 1 b) <1 c) 6.8 d) 0 R

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5. 2- nitropropane on thermal decomposition yields propylene and the rate constant is given by the relationship K = 1.11x1011 e −1(16,4,438/8.3147 )s −1 . For this reaction Arrhenius parameter is a)16, 4438 6.

b) e −16 ,4438

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8.314.

An exactly 1 molal solution of mannitol has a vapour pressure 17.222 mm.of Hg at 20 o C, at the same temperature, the vapor pressure of pure water is 17.535 mm Hg. The activity of water in the given solution is. a) 1 b) 1.1 c) 0.9822 d) zero P

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d) e −16 ,

c) 1.11x10 6

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Ionic strength of 0.1M cesium chloride is a) 0.2 b) 0.05 c) 0.1

d) 1

Contribution to the character by C 5 axis is a) 0.61 b) 1.62 c) 1

d) 0

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For real gases RT – PV / P = ________ a) α b) a c) b d) a 2 /V P

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10. The point group of tetramethyl 1,3,5,7-cycloctatetraene a) D 4h b) D 4d c) C 4v d) S 4 R

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II. Fill up the blanks:11. Number of Oxygen molecules present in 1 Cm 3 at 27 0 C and 101.3 k Pa is ----------. P

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12. Reduced mass of CO 2 is _______ R

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13. Number of fundamental vibration in HCN molecule is _______ 14. Number of classes is equal to ______________

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15. For a reaction N 2 (COO) 2 + H 3 O ------◊ product the plot of ln Ks Vs √μ is ________ with _______ slope. R

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III. True or False:16. For the reaction S2 O82− + 2 I −1 → 2 SO42− + I 2 the addition of KNO 3 decreases the rate constant. R

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17. At standard state f=p=2 18. Chemical potential is an intensive property. 19. Asymmetric stretching in water molecule is represented by B 1. R

20. S33 = E . SECTION - B (10X2=20) Answer any TEN Questions 21. What is the probability at 500 0 C, the energy of a collision is 164.0 KJ. P

22. Arrive at ΔG

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and ΔS

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for ideal solutions.

23. State the properties of a group. 24. Relate E.M.F with activity and activity coefficient. 25. Show that symmetry elements C31C32 of NH 3 belong to the same class. 26. The experimentally determined energy of activation for the decomposition of HI is 184 KJ mol -1. Calculate the energy of activation at 400 0 C according to the collision theory expression. P

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27. Write the significance of σ and l values. 28. Arrive at any two thermodynamic conditions for ideal solution. 29. Assign symmetry elements of methane and benzene molecules. 30. Form the multiplication table for C 2V point group. R

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31. For a given reaction the chemical potential � = -6.24+2x10 -2 T -3x10 -5 T 2 . Calculate its partial molar entropy. P

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32. State great orthogonality theorem. SECTION – C (5X7=35) Answer any FIVE Questions 33. a) Calculate the rate constant for the decomposition of HI at 556 K, using the collision theory formula, given the energy of activation to be 184.2 KJ mol -1 . Compare this valure with the experimental valure of 3.5 x 10 -7 l mol -1 s -1 . The collision diameter of HI may be taken to be 3.5 x 10 -8 cm. (2.5) P

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b) The rate constant of the forward reaction is a reversible reaction & is doubled when the temperature is raised from 27 0 C to 37 0 C. The enthalpy change of the reaction is – 83.6 KJ. Calculate the activation energy of the reaction. (2.5) P

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c) It is observed that with the same reaction mixture 10% of reaction taken place in 15 minutes at 40 0 C and in 3 minutes at 60 0 C. Estimate the energy of activation for this reaction (2) P

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34. a) Derive Gibbs Duhem equation and show that µ1 = − µ2

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dx2 dx1

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b) Write the method of determination of activity and activity coefficient for electrolytes by EMF method.

(3)

35. a) Write ARRT for a bimolecular reaction.

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b) The pre-exponential terms for unimolecular reactions occurring o (3) at 200o C is 2.75 x1015 C , calculate entropy of activation. 36. a) The per exponential term for a bimolecular gas reaction occurring at 300°C are 7.4x10 10 dm 3 mol -1 s -1 . Calculate its entropy of activation. P

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b) Assuming r A = 2.0x10 -10 m and r B = 3.0x10 -10 m and that a reaction between A and B is occurring at 298K in water (viscosity = 0.9x10 -3 Nm -2 s). Calculate the rate constant in m 3 mol -1 s -1 , if the reaction is diffusion controlled. (2) R

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c) At 30°C in 80% ethanol, the rate constant in dm 3 mol -1 s -1 for alkaline hydrolysis of m-chloroethylbenzoate and pmethoxyethylbenzoate are 0.454 and 0.0114 respectively. Given that � values of m-Cl and p-OMe are +0.37 and -0.27 respectively, Calculate a) The reaction constant ρ and b) Rate constant for the alkaline hydrolysis of ethyl benzoate and p-nitroethyl benzoate(� p for -NO 2 = +0.78) (3) P

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37. a) Assign irreducible representation for n, π, π* orbitals of formaldehyde. b) Determine the point groups of. i) CH 4 ii) XeF 4 iii) BF 3 R

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iv) SF 6

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v) NH 3 (4) R

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38. a) Determine the vibrational modes of water molecule and assign each vibration (4) b) Why in formaldehyde π → π * transition is allowed but n →� * is forbidden? (3) P

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39. a) Show that C31 C32 that are conjugate to one another and of same class. (1) b) Write the Great Orthogonality Theorem.

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c) Write the five corollaries of GOT

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d) Show that �Xi(R) 2 = h for △ 2 irreducible representation of C 2V point group.

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e) Assign the Mulliken symbol for the irreducible representation E C2 �V � V’ Γi 1 -1 -1 1 (1) Γi R

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f) Calculate the contribution to the character by S n symmetry element (1) R

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