Avogadro’s hypothesis: “Equal volumes of all gases under similar conditions of temperature and pressure contain equal number of molecules.” Avogadro hypothesis has been found to explain as follows,
(i) Provides a method to determine the atomic weight of gaseous elements.
(ii) Provides a relationship between vapour density (V.D.) and molecular masses of substances.
Molecular mass = 2× vapour density
(iii) It helps in the determination of mass of fixed volume of a particular gas.
Mass of 1 ml gas = V.D. × 0.0000897 gm.
(iv) It also helps in the determination of molar volume at N.T.P.
∴ V.D. × 0.0000897 gm. gas has volume = 1 ml
∴ 2 × V.D.(i.e., molecular mass) gm. has Volume = (1×2×V.D./V.D.×0.0000897) ml = 22400ml
∴ Molar mass of a gas or its 1 mole occupies 22.4 L volume at S.T.P.
(v) It helps in determination of molecular formulae of gases and is very useful in gas analysis. By knowing the molecular volumes of reactants and products of reaction, molecular composition can be determined easily.