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6.6 Avogadro’s Law

Avogadro’s Law states that "equal volumes of different gases

under the same conditions of temperature and pressure contain an equal number of molecules."

Applications of Avogadro’s law :

a) To find out the atomicity of gases : (number of atoms within

a molecule )

Consider formation of hydrogen bromide

Hydrogen + Bromine ® Hydrogen bromide

1 vol            1 vol             2 vol (experimentally found)

\ n molecules n molecules 2n molecules (Avogadro’s law)

\ ˝ molecule ˝ molecule 1 molecule

(Dividing everything by 2n)

Since 1 molecule of hydrogen bromide contains only one atom of hydrogen ˝ molecule of hydrogen contain one atom of hydrogen.

\ 1 molecule of hydrogen contains 2 atoms of hydrogen.

\ H2 is diatomic gas and represented by formula H2

Similarly the formula for Chlorine is Cl

In the same way by considering the reaction such as

Hydrogen + Oxygen ® Steam

    2 vol          1 vol        2 vol

& Nitrogen + Hydrogen ® Ammonia

    1 vol          3 vol                  2 vol

It can be concluded that molecular formula of oxygen gas is O2 and that of nitrogen is N2


6.1 The Gaseous States Properties
6.2 Boyle's Law
6.3 Charle's Law
6.4 Pressure - Temperature Law
6.5 Gay Lussac's Law
6.6 Avogadro's Law
6.7 Graham's Law of Diffusion
6.8 General Gas Equation

Chapter 7

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