Freezing-point depression

The freezing-point depression (ぎょうこてんこうか, Freezing-point depression) is the phenomenon that the freezing point of the solvent lowers when I dissolve a nonvolatile solute in a solvent. For example, the water freezes at zero degree, but does not freeze when salt water and the sugared water do not become colder. If it is a saturated salt solution (salt solution of 25% of salt density), the salt solution freezes only after it becomes -22 degrees Celsius. The freezing-point depression obeys the next expression thermodynamically [¹].

${\displaystyle \Delta T={\frac {MRT_{f}^{2}}{\Delta H_{f}}}m=K_{f}m}$

${\displaystyle \Delta T}$ Cryoscopic size

${\displaystyle m}$ Mass molar concentration of the solute particle

${\displaystyle M}$　Molecular weight of the solvent

${\displaystyle R}$　Gas constant

${\displaystyle T_{f}}$　The freezing point of the solvent

${\displaystyle \Delta H_{f}}$　Heat of solidification (latent heat) of the solvent

These relations are called a colligative property according to a similar expression in the elevation of boiling point.

In other words, with the specific solvent ${\displaystyle K_{f}}$ With the solution thin enough which it becomes the は fixed number, and is called molar freezing-point depression, and dissolved the nonvolatile solute which is solid-phase, and is not taken in of the solvent, the freezing-point depression degree is mass molar concentration of the solutes regardless of the kind of the solute ${\displaystyle m}$ に is proportional. The freezing point of the solution ${\displaystyle T}$ The freezing point of は 純溶媒 ${\displaystyle T_{f}}$ I am expressed in expressions less than として. But a solute is a ceremony passed under the dissociation and the supposition not to associate and must use the density that considered the number of all particles to produce by dissociation when I dissociate it into an ion. I introduce a factor (English version) of ファントホッフ and revise it.

${\displaystyle T\ =\ T_{f}-\Delta T}$

${\displaystyle T\ =\ T_{f}-K_{f}m}$

However, a solute of the solvent when is solid-phase, and is busy, may rise when the freezing point descends.

There were the times when I decided molecular weight than molar mass derived using this property, but is not common classically in today.

Applied

I can use it as a melting snow agent that ice melts by freezing-point depression under the freezing point and drifts to the street when I bind snow piled up with salt.

References

1. ^ Naomichi Iso, Takayoshi Uematsu, Kiyoshi Mashita, sum Toru Inouchi "basics physical chemistry" Tokyo education and researches company, 1997

Allied item

• Osmotic pressure
• Elevation of boiling point
• Vapor pressure descent

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