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Molal Freezing Point Depression Constants

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Publication 13470

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The freezing point of a liquid is the temperature at which the forces of attraction among molecules are just enough to cause a phase change from the liquid state to the solid state. It is the temperature at which the liquid and solid phases exist in equilibrium. The solvent molecules in a solution are somewhat more separated from each other than they are in a pure solvent due to the interference of solute particles. Therefore, the temperature of a solution must be lowered below the freezing point of the pure solvent in order to freeze it. The freezing point depression (ΔTf) of solutions of nonelectrolytes has been found to be equal to the molality (m) of the solute times a proportionality constant called the molal freezing point depression constant (Kf). Therefore, {13470_Introduction_Equation_1} where m is the number of moles of solute per kilograms of solvent.