We know that
P1 = x1 P10 ...(i)
The reduction in the vapour pressure of solvent (ΔP1) is given as
ΔP1 = P10 - P1 = P10 - P10x1 = P10(1-x1)
Knowing that x2 = 1 - x1 from equation (ii) reduces to
ΔP1 = x1P10 ....(iii)
In a solution containing several non-volatile solutes, the lowering of the vapour pressure depends on the sum of the mole fraction of different solutes.
Equation (iii) can be written as
The expression on the left hand ride of the equation is called relative lowering of vapour pressure and is equal to mole fraction of the solute.
Here n1 and n2 are the number of moles of solvent and solute respectively present in the solution.
