3. Suppose the amount of a gas is increased, we can say that there are more
gas molecules. An increase in the number of molecules will cause an increase
in the number of impacts that these molecules will make on the walls of the
container. If this happens, the pressure of the gas inside the container will
increase. The pressure inside the container becomes greater than the pressure
outside the walls. This causes the walls to move outward. Since there is more
wall space, the impact will lessen and the pressure will return to its original
value.
Through this simple demonstration, Amedeo Avogadro was able to
establish the relationship between the number of moles and the volume given
that the pressure and temperature are held constant. Avogadro’s law states
that the number of moles is directly proportional to the volume of gas at a
constant temperature and pressure.
4. Mathematically, we can express this relationship as:
V ∝ n
V = k4n
Where k4 is the constant proportionality. By simultaneously finding for the
formula,
k4 =
𝑉
𝑛
For a given sample of gas under two different sets of condition, at a
constant temperature and pressure,
𝑉
𝑛1
= k4 =
𝑉2
𝑛2
5. Finally, Avogadro’s law is expressed as:
𝑽𝟏
𝒏𝟏
=
𝑽𝟐
𝒏𝟐
The graph of Avogadro’s law is the same as the graph of Charles’ and Gay-
Lussac’s Law, since the volume and the number of moles are directly
proportional to each other.
6. Example 1.
If 0.30 mol of Argon gas occupies a volume of 75 mL at a particular
temperature and pressure, what volume would 0.50 mol ofArgon have under
the same condition?
Given:
V1 = 75 mL V2 = ?
n1 = 0.30 mol n2 = o.50 mol
7. Solution:
𝑽𝟏
𝒏𝟏
=
𝑽𝟐
𝒏𝟐
V2 =
𝑉1
𝑛2
𝑛1
V2 =
(75𝑚𝐿)(0.50 𝑚𝑜𝑙)
(0.30 𝑚𝑜𝑙)
= 125 mL
Interpretation:
As stated, the number of volume is directly proportional to the moles.Thus,
the number of mole increases from 0.30 mol to 0.50 mol, the volume also
increases from 75 mL to 125 mL.
8. Example 2.
A 2. 0 moles of gas occupies an adjustable container with a
volume of 50 L at a particular temperature and pressure. If 0. 8 mole
of gas leaks out, what volume occupy if the temperature and
pressure remain constant?
Given:
V1 = 50 L V2 = ?
n1 = 2.0 mol n2 = 2.0 mol – 0.8 mol (gas leaks) = 1.2 mol
