Freezing-point depression
Freezing-point depression lowers the freezing temperature of a solvent.
Freezing-point depression is a phenomenon in which the temperature at which a substance freezes is lowered by the addition of a smaller amount of another, non-volatile substance. This colligative property arises from a reduction in the chemical potential of the solvent in the mixture, leading to a lower freezing point compared to the pure solvent. It has numerous practical applications, including de-icing roads, antifreeze in automobiles, and the survival of certain organisms in extreme cold.
- field
- Physical chemistry
- known_for
- Lowering of freezing point by solute addition; colligative property; cryoscopy
- applications
- De-icing roads, antifreeze, ice cream making, solder, purity analysis, dairy testing
Lore & Background
Freezing-point depression occurs when a non-volatile solute is added to a volatile liquid solvent, reducing the solution's vapor pressure. This causes the solid and liquid phases to reach equilibrium at a lower temperature than with the pure solvent. The effect is explained by the lowering of the chemical potential of the solvent, which is proportional to the natural logarithm of the mole fraction. This lowering is an entropy effect, as the greater randomness of the solution opposes freezing, requiring a lower temperature for equilibrium.
Reader's Guide
Freezing-point depression is a colligative property with wide-ranging practical significance. It is used in automobile antifreeze (ethylene or propylene glycol in water), road salting (sodium chloride, calcium chloride, or magnesium chloride), and in ice cream makers. Some organisms, such as the rainbow smelt and spring peeper frog, produce antifreeze compounds like glycerol or glucose to survive freezing conditions. In the laboratory, freezing-point depression is employed in cryoscopy to measure molar mass or degree of dissociation, and in differential scanning calorimetry for purity analysis.
Did You Know?
- Freezing-point depression causes sea water to remain liquid at temperatures below 0 °C (32 °F), the freezing point of pure water.
- Sodium chloride can depress the freezing point of water to about −21 °C (−6 °F).
- The spring peeper frog (Pseudacris crucifer) releases massive amounts of glucose into its blood in response to freezing temperatures.
More in Physical Chemistry And Thermodynamics 1-20
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record