PARTIAL PRESSURE -DALTON'S LAW OF PARTIAL PRESSURE

DALTON'S LAW OF PARTIAL PRESSURE

PARTIAL PRESSURE

In a mixture of different gases which do not react chemically each gas behaves independently of the other gases and exerts its own pressure. This individual pressure that a gas exerts in a mixture of gases is called it's partial pressure.

DALTON'S LAW OF PARTIAL PRESSURE

Based on this behaviour of gases, JOHN DALTON formulated a basic law which is known as "The Dalton's law of partial pressure" .

The law states that:

"If two or more gases (which do not react with each other) are enclosed in a vessel,
the total pressure exerted by them is equal to the sum of their partial pressure".

MATHEMATICAL REPRESENTATION

Consider a mixture of three non-reacting gases a , b and c .Partial pressures of these gases are P_a ,P_b and P_c .According to Dalton's law of partial pressure, their total pressure is given by:

P_total = P_a + P_b + P_c

DALTON'S LAW IN THE LIGHT OF KINETIC MOLECULAR THEORY

According to kinetic molecular theory of gases there is no force of attraction or repulsion among the gas molecules. Thus each gas behaves independently in a mixture and exerts it's own pressure.
In terms of KINETIC MOLECULAR THEORY, Dalton's law of partial pressure can be explained as:

"In a non-reacting mixture of gases, each gas exerts separate pressure on the container in which it is confined due to collision of it's molecules with the walls of container.
The total pressure exerted by the gaseous mixture is equal to
the sum of collisions of the molecules of individual gas ."

EXPRESSION FOR PARTIAL PRESSURE

Consider a gaseous mixture of three different gases a , b and c enclosed in a container of volume Vdm³ at T Kelvin. Let the partial pressures of these gases are P_a ,P_b and P_crespectively and total pressure of mixture is P_t. Let there are n_a ,n_b and n_c moles of each gas respectively and the total number of
moles are n_t.

Three gases confined in a cylinder under similar conditions: