What is the Difference Between Melting Point and Freezing Point?

The melting point and freezing point are actually the same temperature, but they describe different processes occurring at the same temperature.

• Melting Point: This is the temperature at which a solid substance changes to a liquid state under normal atmospheric pressure. When a solid reaches its melting point, it begins to melt, and its temperature remains constant during the entire melting process.
• Freezing Point: This is the temperature at which a liquid substance changes to a solid state under normal atmospheric pressure. When a liquid reaches its freezing point, it begins to freeze, and its temperature remains constant during the entire freezing process.

In theory, the melting point of a solid should be the same as the freezing point of the liquid, and in most cases, they are equal. The equality of melting and freezing points is essential for thermodynamic equilibrium, as a difference between the two would create a perpetual motion machine of the first kind.

Comparative Table: Melting Point vs Freezing Point

The main difference between melting point and freezing point lies in the process they describe:

For pure, crystalline solids, the melting point and freezing point are often the same or very close. However, for mixtures, the melting point can be lower than the freezing point. Additionally, the transition between the solid and liquid states can be sharp for small samples of pure substances, while mixtures tend to melt over a broad temperature range.