Freezing point of a substance is the temperature at which the solid and liquid forms of the substance are in equilibrium and their vapour pressures are equal. Freezing point of solution is always lower than that of the pure solvent.
Due to lower vapour pressure of the solution, solid from a solution separates out at lower temperature. The decrease is called the depression in freezing point.
ΔTf = \(T^0_f\) - Tf
\(T^0_f\) = freezing point of pure solvent
Tf = freezing point of solution
Depression in freezing point is given by equation :
ΔTf = Kf .m
Kf = molal depression contant / cryoscopic constant
If m = 1 , ΔTf = Kf
Molal Depression Constant
Depression in freezing point when molality of solution is unity.
SI unit = K kg mol-1
Relationship between molal depression constant and enthalpy of fusion
Relationship between molal depression constant and latent heat of fusion
