Important Questions for CSIR NET Chemical Science 2023 - Physical Chemistry!

Most Important Questions On Physical Chemistry - Download PDF

1. A cricket ball has a weight of 100 g is located within 1 nm. Determine the uncertainty in the
velocity.
A. 5.27×10 -23 m/s
B. 5.27×10 -25 m/s
C. 5.27×10 -24 m/s
D. 5.27×10 -27 m/s

2. The extent of dissociation of PCl 5 at a certain temperature is 20% at one atm pressure. Calculate
the pressure at which this substance is half-dissociated at the same temperature.
A. 0.123
B. 0.389
C. 0.423
D. 0.789

3. KNO 3 crystallizes in an orthorhombic system with the unit cell dimensions a = 542 pm, b = 917 pm
and c = 645 pm. Calculate the diffraction angles for first-order X-ray reflections from 100 planes
using radiation with wavelength = 154.1 pm.
A. 8 0 10’
B. 9 0 20’
C. 4 0 40’
D. 3 0 30’

4. Determine the temperature at which the average velocity of oxygen equals that of hydrogen at 20
K.
A. 420 K
B. 300 K
C. 320 K
D. 500 K

5. Acetaldehyde (CH 3 CHO) decomposes by second-order kinetics with a rate constant of 0.334 M –1 s –1
at 500°C. The time it would take for 80% of the acetaldehyde to decompose in a sample that has an initial concentration of 0.00750 M is
A. ~ 1600 sec
B. ~ 1850 sec
C. ~ 1000 sec
D. ~ 5100 sec

6. The time for which the oxygen atom remains adsorbed on a tungsten surface is 0.36 s at 2550 K
and 3.49 s at 2360 K. Determine the activation of desorption of oxygen atom.
A. 432.42 kJ/mol
B. 532.30 kJ/mol
C. 326.43 kJ/mol
D. 598.29 kJ/mol

7. For a homogeneous gaseous reaction,
SO 2 Cl 2 → SO 2 + Cl 2
that obeys first-order reaction, the half-life is 8.0 minutes. How long will it take for the concentration
of SO 2 Cl 2 to be reduced to 1% of the initial value?
A. 46.92 min
B. 52.93 min
C. 32.61 min
D. 23.43 min

8. At what wavelength in Å would the anti-stokes line appear in the Raman spectrum of the sample
excited by the 4358 Å line of mercury. A Raman line was observed at 4447 Å.
A. 6238
B. 4272
C. 5678
D. 3456

9. Determine the molar solubility of Zn(OH) 2 in 1 M ammonia solution at room temperature.

A. 4.19×10 -4
B. 4.19×10 -5
C. 4.19×10 -6
D. 4.19×10 -3

10. Point group which is both polar and optically active is:
A. C i
B. C s
C. C 1
D. C

Answer Key

1. B
2. A
3. A
4. C
5. A
6. D
7. B
8. B
9. D
10. C

Solutions:

Solution 1. According to the uncertainty principle

Solution 2. Kp = α2P/(1 – α2)

P = 1 atm, α = 0.2

 Kp = (0.2)2 (1 atm) / (1 – 0.04) = 0.041 atm

Let P' be the pressure at which α = 0.5, then

Kp = α2P'/(1 – α2)

0.041 atm = (0.5)2P'/(1 – 0.25)

P = 0.123 atm

Solution 3. Bragg’s equation is:

2dhkl sin θ = nλ

For an orthorhombic system,

1/(dhkl)2 = (h2/a2) + (k2/b2) + (l2/c2)

∴   1/(d100)2 = (1/542 pm)2 + (0/917 pm)2 + (0/645 pm)2 = (1/542 pm)2

∴   d100 = a = 542 pm

For first order reflection, n = 1.

Also,

λ = 154.1 pm

∴  where θ100 = 8°10′

Solution 4. The expression to calculate average velocity is:

<c> = (8RT/πM)1/2, i.e., <c> ∝ (T/M)1/2

Let <c>1 and <c>2 be the average velocities of O2 and H2, respectively.

Solution 6. The expression to calculate desorption of oxygen atom is:

Solution 8. The anti-Stokes line will appear at a frequency 460 cm–1 higher than the frequency (in cm–1) associated with the 4358 Å Hg line used as a source of excitation. Now, 

Solution 9. The solubility equilibrium, in this case, is represented as:

Solution 10. For a point group that is to be both optically active and polar, it should not have any inversion center. Ci cannot be the answer. The molecule should not have any sigma plane, otherwise, the molecule will be asymmetric asymmetric molecules are optically inactive, but they are polar molecules so, Cs and C2v cannot be the answer because we need a point group that is not polar, and optically inactive. So, according to this, c is the correct option.

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• Study Notes for CSIR NET Life Science - (Download PDF)
• Study Notes for CSIR NET Chemical Science - Download PDF Here!

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