The lowering of vapour pressure of a solution causes a lowering of the freezing point compared to that of the pure solvent.
According to Raoult’* law, when a non-volatile solid is added to the solvent its vapour pressure decreases and now it would become equal to that of solid solvent at lower temperature. Thus, the freezing point of the solvent decreases.
T0f is the freezing point of pure liquid solvent. Tf is the freezing point of solution.
