Question
State Avogadro's law and prove that volume of gases at constant temperature and pressure is directly proportional to their number of moles.
Solution
Avogadro’s law states: Equal volumes of all gases at the same temperature and pressure contain the same number of molecules.
For example, 22·4 litres of any gas at STP (273K and 760mm Hg) contain Avogadro number, N0 (6·02×1023) of molecules irrespective of its nature.
It follows that volume of gas V is directly proportional to N, the number of molecules at constant temperature and pressure.
V ∝ N (at constant temperature and pressure)
Also number of moles of a gas (n) ∝ number of molecules (N)
Hence the volume of gases at constant temperature and pressure is directly proportional to their number of moles.
