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## Chapter: 10th Science : Chapter 7 : Atoms and Molecules

The AvogadroÔÇÖs law states that ÔÇťequal volumes┬ş of all gases under similar conditions of temperature and pressure contain equal number of moleculesÔÇŁ

In 1811 Avogadro framed a hypothesis based on the relationship between the ┬şnumber of molecules present in equal volumes of gases in different conditions┬ş.

The AvogadroÔÇÖs law states that ÔÇťequal volumes┬ş of all gases under similar conditions of temperature and pressure contain equal number of moleculesÔÇŁ

It follows that the volume of any given gas must be proportional to the number of molecules in it. If ÔÇśVÔÇÖ is the volume and ÔÇśnÔÇÖ is the number of molecules of a gas, then Avogadro law is represented, mathematically, as follows:

V ╬▒ n

V = constant ├Ś n

Thus, one litre (1 dm3) of hydrogen contains the same number of molecules as in one litre of oxygen, i.e. the volume of the gas is directly proportional to the number of molecules of the gas. ## Explanation

Let us consider the reaction between ┬şhydrogen and chlorine to form hydrogen chloride gas

H2(g) + Cl2(g) Ôćĺ 2 HCl(g)

1 vol + 1 vol Ôćĺ 2 volumes

According to AvogadroÔÇÖs law 1 volume of any gas is occupied by ÔÇťnÔÇŁ number of molecules. n molecules + n molecules Ôćĺ 2n molecules

if n = 1 then

1molecule + 1 molecule Ôćĺ 2 molecules.

molecule + ┬Ż molecule Ôćĺ 1 molecule

1 molecule of hydrogen chloride gas is made up of ┬Ż molecule of hydrogen and ┬Ż molecule of chlorine. Hence, the molecules can be subdivided. This law is in agreement with DaltonÔÇÖs atomic theory.

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10th Science : Chapter 7 : Atoms and Molecules : Avogadro Hypothesis |