When a non volatile solute is added to a pure solvent at its boiling point, the vapour pressure of the solution is lowered below 1 atm. To bring the vapour pressure again to 1 atm the temperature of the solution has to be increased.
As a result, the solution boils at a higher temperature (Tb) than the boiling point of the pure solvent (T°b ). This increase in the boiling point is known as elevation of boiling point ∆Tb = Tb – T°b .
