Questions - Answers
1. Explain different terms in Vander Waals equation.
A:
a & b = Vander Waals constants
n = no. of moles
P = pressure
V = volume
T = absolute temperature
R = Universal gas constant
2. Which gas diffuses faster among N2, O2, CH4 gases? Why?
A: CH4 diffuses faster among all these gases due to its low molecular weight (16). According to Graham's law of diffusion, rate of diffusion of a gas is inversely proportional to its molecular weight.
3. What are 'isotherms'?
A: The curves obtained when a graph is plotted between pressure and volume at constant Temperature.
4. What are STP conditions?
A: Standard conditions of Temperature (273.15 K) and pressure (1 atmosphere or 760 mm of Hg) are called STP conditions.
5. Give the values of Gas constant in different Units.
A: R = 8.314 × 107 Ergs mole−1 K−1
R = 8.314 Joules mole−1 K−1
R = 1.987 Cals mole−1 K−1
R = 0.083 bar dm3 mole−1 K−1
6. What is boltzman's constant? give its value.
A: The Gas constant per one molecule of a Gas.
K = 1.38 × 10−16 Ergs K−1 molecule−1
K = 1.38 × 10−23 Joules K−1 molecule−1
7. Ammonia gas diffuses through a fine hole at the rate 0.5 lit/min. Under the same conditions find the rate of diffusion of Chlorine gas.
A:
8. Write important postulates of kinetic molecular theory of gases?
A: Kinetic molecular theory of gases: Boltzmann, Maxwell, Clasius proposed this theory to explain observed facts of the gaseous state. Main postulates of this theory are: Tiny particles present in a gas are called 'molecules'.
Molecules move randomly in all the directions. Attractions or repulsions are not observed between the molecules. Molecular motions are unaffected by gravitational force. Molecular collisions are perfectly elastic. Volume of individual molecule is negligible compared to the volume of the vessel. Pressure exerted by the gas is due to the collisions made on the walls of the vessel. Average kinetic energy is directly proportional to absolute temperature (T). Only ideal gases obey this theory.
9. Derive ideal gas equation from gas laws.
A: The equation that indicates the effect of P, V, T and no. of moles on a gaseous system.
According to Boyle's law V α 
....... (1)
According to Charles law V α T ....... (2)
According to Avogadro's law V α n ...... (3)
from (1), (2), (3) V α 
P V α nT ∴ PV = nTR
10. State Graham's law of diffusion. 100 cm3 of CO2 gas is diffused in 25 seconds through a porous membrane. How much time does the same volume of SO2 to diffusion?
A: The rate of diffusion of a gas is inversely proportional to the square root of its density r α 
= 30.15 sec
11. State Dalton's law of partial pressures. Find the partial pressure of each gas in a mixture containing 4.4 grams of CO2 and 5.6 grams of N2 present, at a pressure of 1.5 atm at a given temperature.
A: At constant temperature, total pressure of mixture of non reacting gases is equal to partial pressures of the component gases.
12. Deduce a) Graham's law and b) Dalton's law from Kinetic gas euqation.
A: a) Graham's law:
b) Dalton's law:
