The key difference between freezing point and freezing point depression is that freezing point is the temperature at which a liquid becomes a solid, whereas freezing point depression is the decrease of the freezing point of a solvent due to the addition of a solute into the solvent.
Freezing point is a temperature value at which a phase change of matter takes place from liquid to solid phase. Most of the times, it is similar to the melting point of a material at which a solid converts into its liquid state.
CONTENTS
1. Overview and Key Difference
2. What is Freezing Point
3. What is Freezing Point Depression
4. Side by Side Comparison – Freezing Point vs Freezing Point Depression in Tabular Form
6. Summary
What is Freezing Point?
The freezing point is the temperature at which a liquid becomes solid. At the freezing point, liquid to solid transition of the phase of matter occurs at the melting point, the solid phase converts into its liquid phase. Theoretically, the freezing point is equal to the melting point. But practically, we can supercool liquids beyond the freezing point.
We can use the terms freezing and solidification interchangeably, but some authors tend to differentiate between these two terms because freezing occurs due to changes in temperature, while solidification can occur due to changes in pressure as well.
Knowing the freezing point of materials is very important in different applications, including food preservation, where we can inhibit the decay of food and growth of microorganisms, freezing of living organisms or tissues during tissue preservation, etc.
What is Freezing Point Depression?
Freezing point depression is the decrease of the freezing point of a solvent due to the addition of a solute into the solvent. This is a colligative property, meaning freezing point depression depends only on the amount of solutes, not on the nature of the solute. After the freezing point, depression of substance has occurred, the freezing point of the solvent decreases to a lower value than that of the pure solvent. The freezing point depression is the reason why seawater remains in the liquid state even at 0°C (the freezing point of pure water).
However, the added solute should be a non-volatile solute; if not, the solute does not affect the freezing point of the solvent because it gets volatilized easily. This concept can also be used to explain the changes in the freezing point of solid mixtures. Finely powdered solid compounds have a lower freezing point than pure solid compounds when impurities are present (solid-solid mixture).
The freezing point is the temperature at which the vapor pressure of a solvent and the vapor pressure of the solid form of that solvent is equal. If a non-volatile solute is added to this solvent, the vapor pressure of the pure solvent decreases. Then the solid form of the solvent can remain in equilibrium with the solvent even at lower temperatures than the normal freezing point.
What is the Difference Between Freezing Point and Freezing Point Depression?
Freezing point is a temperature value at which a phase change of matter occurs. The key difference between freezing point and freezing point depression is that freezing point is the conversion of liquid phase into solid phase due to change in temperature, whereas freezing point depression is the decrease of the freezing point of a solvent due to the addition of a solute into the solvent.
The below infographic summarizes the differences between freezing point and freezing point depression in tabular form.
Summary – Freezing Point vs Freezing Point Depression
Freezing point is a temperature value, while freeing point depression is an outcome. The key difference between freezing point and freezing point depression is that freezing point is the temperature at which a liquid becomes solid, whereas freezing point depression is the decrease of the freezing point of a solvent due to the addition of a solute into the solvent.
Reference:
1. Helmenstine, Anne Marie. “What Is the Freezing Point of Water?” ThoughtCo, Aug. 28, 2020, Available here.
Image Courtesy:
1. “Light glinting off icicles” By Daler Boi – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Thermometer CF” By Gringer – n /a (Public Domain) via Commons Wikimedia