Английская Википедия:Cryoscopic constant

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Шаблон:Use American English Шаблон:Short description Шаблон:Refimprove In thermodynamics, the cryoscopic constant, Шаблон:Mvar, relates molality to freezing point depression (which is a colligative property). It is the ratio of the latter to the former:

<math>\Delta T_f = -i \cdot K_f \cdot b</math>

• Шаблон:Mvar is the van ‘t Hoff factor, the number of particles the solute splits into or forms when dissolved.
• Шаблон:Mvar is the molality of the solution.

Through cryoscopy, a known constant can be used to calculate an unknown molar mass. The term "cryoscopy" comes from Greek and means "freezing measurement." Freezing point depression is a colligative property, so Шаблон:Math depends only on the number of solute particles dissolved, not the nature of those particles. Cryoscopy is related to ebullioscopy, which determines the same value from the ebullioscopic constant (of boiling point elevation).

The value of Шаблон:Mvar, which depends on the nature of the solvent can be found out by the following equation:

<math>K_{f} = \frac{R \cdot M \cdot T_{f}^{2}}{\Delta_\mathrm{fus}H}</math>

• Шаблон:Mvar is the ideal gas constant
• Шаблон:Mvar is the molar mass of the solvent in kg mol⁻¹
• Шаблон:Mvar is the freezing point of the pure solvent in kelvins
• Шаблон:Math represents the molar enthalpy of fusion of the solvent in J mol⁻¹.

The Шаблон:Mvar for water is 1.853 K kg mol⁻¹.

See also

• List of boiling and freezing information of solvents

References

Шаблон:Thermodynamics-stub