Avogadro Law
Avogadro Law
In 1811
Italian scientist Amedeo Avogadro tried to combine conclusions of Dalton’s
atomic theory and Gay Lussac’s law of combining volumes which is not known as
Avogadro law. It states that equal volumes of all gases under the same
conditions of temperature and pressure contain equal number of molecules.
This means that as long as the temperature and pressure remain constant. The
volume depends upon number of molecules of the gas or in other words amount of
the gas. Mathematically we can write
V ∝ n Where n is the number of
moles of the gas.
⇒ V = k4n
This number
of molecules in one mole of a gas has been determined to be 6.022 1023 and is known as Avogadro
constant. You will find that this is the same number which we came across while
discussing definition of a ‘mole’.
Since volume
of a gas is directly proportional to the number of moles; one mole of each gas
at standard temperature and pressure (STP) will have same volume. Standard
temperature and pressure means 273.15K (0oC) temperature and 1 bar (i.e., exactly 105 pascal) pressure.
These values approximate freezing temperature of water and atmospheric pressure
at sea level. At STP molar volume of an ideal gas or a combination of ideal
gases is 22.71098 L mol-1
Number of
moles of a gas can be calculated as follows
Where m =
mass of the gas under investigation and M = molar mass
Thus,
Equation can
be rearranged as follows :
Here ‘d’ is
the density of the gas. We can conclude from equation that the density of a gas
is directly proportional to its molar mass.
A gas that
follows Boyle’s law, Charles’ law and Avogadro law strictly is called an ideal
gas. Such a gas is hypothetical. It is assumed that intermolecular forces are
not present between the molecules of an ideal gas. Real gases follow these laws
only under certain specific conditions when forces of interaction are
practically negligible. In all other situations these deviate from ideal
behavior.
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