Question

1. a) Band theory is used to explain the conductivity of different solid crystals. Define the band width and calculate s band width assuming there is indefinite number of molecular orbitals in the s band.

b) Explain how metallic conductor, semiconductor and insulator are identified by band theory.

c) 3.0 mol CO2 behaving as a van der Waals gas, when it is confined under the following conditions: at 750 K in 150 cm3.
For CO2 Van der Waals coefficients, a: 3.610 L2 atm mol-2, b: 4.29x10-2 Lmol-1. Gas constant R is 8.206 x 10-2 L atm K-1mol-1
i) Calculate the gas pressure (in atm),

ii) What is the molar volume of the gas (in L/mol),
iii) What is the pressure when it is ideal gas and use it to state dominating force in

the above gas?

2. a) Use one example to describe Born-Haber cycle

b) Calculate
i) The resultant of two stationary dipole moments of magnitude 1.2D and 1.8D that make an angle of 130o to each other in vacuum (expressed in D)

ii) The interaction between pairs of rotating molecules with μ = 1.5D and r =0.1 nm in one material at 325K in air (expressed in kJ/mol)

3. a) Account for two kinds of semiconductor and use schemes to explain charge flow between n-type and p-type semiconductors in the dark condition without a bias

b)A substance known to have a cubic unit cell gives reflections with Cu Karadiation (wavelength 154 pm) at the glancing angle of 32.6o.

The reflection is known to be due to the (220) plane. Index the reflection at the glancing angle of 39.4o
.

Answer 1