In thermodynamics, the cryoscopic constant, , relates

molality Molality is a measure of the number of moles of solute in a solution corresponding to 1 kg or 1000 g of solvent. This contrasts with the definition of molarity which is based on a specified volume of solution. A commonly used unit for molali ...

freezing point depression Freezing-point depression is a drop in the minimum temperature at which a substance freezing, freezes, caused when a smaller amount of another, non-Volatility (chemistry), volatile substance is added. Examples include adding salt into water (u ...

(which is a

colligative property In chemistry, colligative properties are those properties of Solution (chemistry), solutions that depend on the ratio of the number of solute particles to the number of solvent Particle, particles in a solution, and not on the nature of the chemic ...

). It is the ratio of the latter to the former: :

\Delta T_f = -i \cdot K_f \cdot b

* is the

van ‘t Hoff factor A van is a type of road vehicle used for transporting goods or people. Depending on the type of van, it can be bigger or smaller than a pickup truck and SUV, and bigger than a common car. There is some varying in the scope of the word across th ...

, the number of particles the solute splits into or forms when dissolved. * is the

of the solution. Through cryoscopy, a known constant can be used to calculate an unknown

molar mass In chemistry, the molar mass of a chemical compound is defined as the mass of a sample of that compound divided by the amount of substance which is the number of moles in that sample, measured in moles. The molar mass is a bulk, not molecular, p ...

. The term "cryoscopy" comes from

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

and means "freezing measurement." Freezing point depression is a

, so depends only on the number of solute particles dissolved, not the nature of those particles. Cryoscopy is related to

ebullioscopy An ebullioscope (from the Latin ''ēbullīre'' (to boil) + -scope) is an instrument for measuring the boiling point of a liquid. This can be used for determining the alcoholic strength of a mixture, or for determining the molecular weight of a non- ...

, which determines the same value from the

ebullioscopic constant In thermodynamics, the ebullioscopic constant relates molality to boiling point elevation. It is the ratio of the latter to the former: :\Delta T = iK_\text b * is the van 't Hoff factor, the number of particles the solute splits into or forms ...

(of boiling point elevation). The value of , which depends on the nature of the solvent can be found out by the following equation: :

K_ = \frac

* is the

ideal gas constant The molar gas constant (also known as the gas constant, universal gas constant, or ideal gas constant) is denoted by the symbol or . It is the molar equivalent to the Boltzmann constant, expressed in units of energy per temperature increment per ...

* is the

of the solvent in kg mol⁻¹ * is the

freezing point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends ...

of the pure solvent in kelvins * represents the molar

enthalpy of fusion In thermodynamics, the enthalpy of fusion of a substance, also known as (latent) heat of fusion, is the change in its enthalpy resulting from providing energy, typically heat, to a specific quantity of the substance to change its state from a s ...

of the solvent in J mol⁻¹. The for water is 1.853 K kg mol⁻¹.

References

Phase transitions Thermodynamic properties {{Thermodynamics-stub

See also

References