Kinetic Theory – Solutions
1) Estimate the fraction of molecular volume to the actual volume occupied by oxygen gas at STP. Take the diameter of an oxygen molecule to be 3 A.
Radius ‘r’ of an oxygen molecule, r = d/2 = (3/2) A = 1.5 x 10-8 cm
Volume occupied by 1 mole of oxygen gas at STP = 22.4 litres = 22400 cm3
Molecular volume of one mole of oxygen gas, V = πr3 N
Where, N is Avagadro’s number = 6.023 x 1023 molecules/mole
So, V = x 3.14 x (1.5 x 10-8)3 x 6.023 x 1023= 8.51 cm3
Ratio of the molecular volume to the actual volume of oxygen = = 3.8 x 10-4
2) Molar volume is the volume occupied by 1 mole of any (ideal) gas at standard temperature and pressure (STP: 1 atmospheric pressure, 00C). Show that it is 22.4 litres.