answer
Avogadro's law states that, at constant temperature and pressure, the volume of a gas is directly proportional to the number of moles present. In other words, equal volumes of gases at the same pressure and temperature contain the same number of molecules - this is true regardless of their physical properties or chemical nature.
This number of molecules is
6.022
⋅
10
23
and is known as Avogadro's number,
N
A
.
Matematically, Avogadro's law can be written like this
V
n
=
c
o
n
s
t
, or, better yet,
V
1
n
1
=
V
2
n
2
.
Avogadro's law, as well as Boyle's law and Charles' law, are special cases of the ideal gas law,
P
V
=
n
R
T
. If temperature and pressure are kept constant, and knowing that
R
is of course constant, then
P
V
=
n
R
T
→
P
V
n
=
R
T
→
V
n
=
R
T
P
=
c
o
n
s
t
, which represents Avogadro's law.
The ideal gas law can also be written to incorporate
N
A
, since the number of moles are actually the number of molecules divided by Avogadro's number
P
V
=
N
N
A
⋅
R
T
, where
N
represents the number of molecules.