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?

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## (a) The main applications of Avogadro's law are as follows: Explanation of Gay-Lussac's law. Determination of atomicity of gases. Determination of molecular formula of a gaseous compound. Establishment of relationship between the relative vapour density of a gas and its relative molecular mass. 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.

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