Question

(a) What are the main applications of Avogadro's law?
(b) How does Avogadro's law explain Gay-Lussac's law of combining volumes?

Answer 1

(a) The main applications of Avogadro's law are as follows:

1. Explanation of Gay-Lussac's law.

2. Determination of atomicity of gases.

3. Determination of molecular formula of a gaseous compound.

4. Establishment of relationship between the relative vapour density of a gas and its relative molecular mass.

5. Establishment of relationship between gram molecular weight and volume of the gas at STP.

(b) Consider a reaction between hydrogen gas and chlorine gas to form hydrogen chloride gas.
According to Gay-Lussac's law, one volume of hydrogen and one volume of oxygen react to give two volumes of hydrogen chloride gas.
According to Avogadro's law, if one volume of hydrogen contains n molecules of the gas, then one volume of chlorine gas will also contain n molecules of the gas.
${\mathrm{H}}_2+{\mathrm{Cl}}_2\to 2\mathrm{HCl}$
1 volume 1 volume 2 volumes [Gay-Lussac's law]
n molecules n molecules 2n molecules [Avogadro's law]
As we know that hydrogen and chlorine are diatomic gases.
Therefore,
${\mathrm{H}}_2+{\mathrm{Cl}}_2\to 2\mathrm{HCl}$
2 atoms 2 atoms 2 molecules
1 atom 1 atom 1 molecule

Thus, one molecule of hydrogen chloride is formed when one atom of hydrogen combines with one atom of chlorine, which explains the Gay-Lussac's law.