DALTON’S LAW OF PARTIAL PRESSURES
DALTON’S LAW OF PARTIAL PRESSURES:When two or more non-reacting
gases are mixed in a container they tend to behave individually as there are no
interactions between ideally behaving gases. The total pressure of the mixture
is the sum of individual pressures of the three gases. When we say individual
pressure it means the pressure that the gas would have exerted had it been the
only gas in the same container. This pressure is called “Partial Pressure” of a
gas. For example, If sample of a gas A is kept in a container it exerts a
pressure of 2 atm, sample of gas B is kept in the same container and it exerts
3 atm then when the samples are mixed in the same container then the total
pressure exerted is the sum of partial pressures that is 5 atm.
PTOTAL
= PA + PB
This is called “Dalton’s Law”.
Ideal gas equation can be applied
on both the gases.
PAV = nART
PBV = nBRT
Dividing,
PA/PB = nA/nB
=> PA/(PA+PB)
= nA/(nA+nB)
=> PA/PTOTAL
= nA/nTOTAL = XA (mole fraction of A)
Therefore the partial pressure of A,
PA = XAPTOTAL
Always remember Dalton’s
Law is applicable to non-reacting gases only.
