6.6 Avogadro’s Law
Avogadro’s Law states that "equal volumes
of different gases
under the same conditions of temperature and pressure contain an equal number of molecules."
Applications of Avogadro’s law :
a) To find out the atomicity of gases : (number of atoms within
a molecule )
Consider formation of hydrogen bromide
Hydrogen + Bromine ® Hydrogen bromide
1 vol 1 vol 2 vol (experimentally found)
\ n molecules n molecules 2n molecules (Avogadro’s law)
\ ˝ molecule ˝ molecule 1 molecule
(Dividing everything by 2n)
Since 1 molecule of hydrogen bromide contains only one atom of hydrogen ˝ molecule of hydrogen contain one atom of hydrogen.
\ 1 molecule of hydrogen contains 2 atoms of hydrogen.
\ H2 is diatomic gas and represented by formula H2
Similarly the formula for Chlorine is Cl
In the same way by considering the reaction such as
Hydrogen + Oxygen ® Steam
2 vol 1 vol 2 vol
& Nitrogen + Hydrogen ® Ammonia
1 vol 3 vol 2 vol
It can be concluded that molecular formula of oxygen gas is O2 and
that of nitrogen is N2