Dalton’s Law Of Partial Pressure


About Dalton’s Law Of Partial Pressure

In 1801, Dalton’s found that when two or more gases are placed in same container,this observation is summarized in Dalton’s Law Of Partial Pressure


The total pressure of a gaseous mixture is the sum of the partial pressure, exerted by each of the gases present in the mixture

Mathematic Expression:

Mathematically this law can be expressed as,
P = P1 + P2 + P3 + ………………
Where P = Total pressure of gaseous mixture
P1 = Partial Pressure of gas 1.
P2 = Partial Pressure of gas 2.
P3 = Partial Pressure of gas 3.


When two or more gases which do not react chemically, are mixed in the same container, then each gas will exert the same pressure as it would exert if it alone occupied the volume containing the mixed gases, under the same condition. This portion of the total pressure of a mixture is known as PARTIAL PRESSURE. Dalton observed that the total pressure of a mixture of different gases is always equal to the sum of individual or partial pressure of each gas present in a mixtureDalton's Law Of Partial Pressure

Experimental Verification:

Let us suppose that two different gases A & B are confined in two separate compartments as shown, in the figure. Both the compartments are of same size with a pressure measuring device.
Now suppose that the pressure of a gas is ‘A’ is 800 torr and that of gas ‘B’ is 900 torr in their separate compartments. If gas ‘A’ was transferred into the compartment ‘B’ with the help of a movable piston through the total pressure in this compartment would be the sum of the original pressure in the two compartments when the gases were occupying same volume separately.
i.e. Ptotal = PA + PB
1700 = 800 + 900
1700 = 1700
Hence, law is verified.

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