3 Vapour
Pressure of
Solutions of
Solids in
Liquids
Fig 1 4: Decrease in the vapour pressure of the
solvent on account of the  presence of
solute in the solvent (a) evaporation of the
molecules of the solvent from its surface
is denoted by 
, (b) in a solution, solute
particles have been denoted by  and they
also occupy part of the surface area Rationalised 2023-24
13
Solutions
the vapour pressure of the solvent, x1 be
its mole fraction, pi
0 be its vapour pressure
in the pure state