Avogadro's hypothesis Law Principle- Berzelius, a chemist tried to correlate Dalton's atomic theory & Gay-Lussac's Law of gaseous volumes. According to his Berzelius hypothesis Equal volumes of all gases under similar conditions of temperature & pressure contain equal number of atoms e.g.
Hydrogen (1 vol) + Chlorine (1 vol)->HCl (2 vol)
Acc to Berzelius hypothesis:
Hydrogen (1/2 atom) + Chlorine (1/2 atom)->HCl (1 compound atom)
But this is indirect conflict of Dalton's atomic theory, so it was rejected.
So a new hypothesis was given by Avogardo.
According to him, An atom is a smallest particle of an element which can take part in a chemical reaction which may or may not be capable of independent existence.
A molecule is the smallest particle of an element or of a compound which have an independent existence. So the smallest particle of a gas is a molecule not an atom, so the volume of gas must be related to the number of molecules rather than atoms.
According to Avogrado's Hypothesis-Equal volume of all gases under similar conditions of temperature & pressure contain equal number of molecules. This is able to explain all the gaseous reactions & now known as Avogrado's Law or Avogrado's principle.
For example-
Hydrogen (1 vol) + Chlorine (1 vol)->HCl (2 vol)
By Avogrado's hypothesis:
n molecule+n molecule gives 2n molecule
1/2molecule of both [Hydrogen + Chlorine] ->HCl (1 molecule)
Applications of this hypothesis-
(1)In the calculation of atomicity of elementary gases-Atomicity is defined as the number of atoms of the element present in one molecule of the substance e.g. atomicity of N2 is two & O3 is three.
(2)To find the relationship between molecular mass & vapour density of gas-(relative density)
Vapour density of gas=Density of gas/density of hydrogen
=Mass of [certain vol of gas/same volume of H2] at STP
=Mass of [n molecule of gas/ n molecule of H2] at STP
=Mass of [1 molecule of gas/ 1 molecule of H2] at STP
Vapour density=Molecular Mass/2
(3)To find the relationship between mass & volume of gas-As the
Molecular Mass=Vapour density x 2
Or Molecular Mass=Mass of 22.4 L of gas at STP
Thus 22.4 L of any gas at STP weight is equal to the molecular mass of the gas expressed in grams which is called Gram-Molecular Volume Law (G.M.V.).