Daltons law is an extension of the ideal gas laws and valid only for unreactive gases.

1. Dalton’s law
By Andrew Samupindi
21PGTE004

2. The law of partial pressures
• This was formulated by John Dalton in 1801 and is related to the ideal gas laws...
• It states that : In a mixture of non reactive gases , the total pressure exerted Is equal
to the sum of partial pressures at individual gases.

3. Ideal gas law
From the ideal gas equation, PV= nRT,
We can surmise that the behaviour of all ideal gases depends on the total number of
moles no matter the identity.
At the same temperature and volume, the pressure of a gas A in a container can be
expressed as : Pₐ=
𝑛ₐ𝑅𝑇
𝑉
For a mixture of gases, we can write:
Pₜ=
𝑛ₐ𝑅𝑇
𝑉
+
𝑛ₜ𝑅𝑇
𝑉
+
𝑛ₜ𝑅𝑇
𝑉
Therefore total pressure due to gases : (Pt) =Pa +Pm +Ps

4. Dalton’s law
• Each gas exerts a fraction of the total pressure.
• The gases all behave independently from each other.
• MOLAR FRACTION
• Pₐ=
𝑛ₐ𝑅𝑇
𝑉
, Pₜ =
𝑛ₜ𝑅𝑇
𝑉
diving these two we get :
•
Pₐ
Pₜ
=
𝑛ₐ
𝑛ₜ
=Xb(Molar fraction)
• Therefore Pₐ=XbPₜ ;
• If we multiply the mole fraction of a gas by the total pressure in
the container we can obtain the “partial pressure of the gas.”

5. Dalton’s law of partial pressures
Assume we have two containers with the same volume and the same number of gas
particles ie (moles of gas) At the same temperature and volume both the pure gas and
the sum total of partial pressures will exert the same pressure.
Air = ∑(oxygen+ nitrogen +Argon +water + carbon dioxide)..

6. Thank You