Here's why:
* Freezing is the process of a liquid changing into a solid.
* Melting is the process of a solid changing into a liquid.
These are essentially the *reverse* of each other. At the specific temperature where these transitions occur, the substance is in equilibrium between its solid and liquid phases. This means that the rate of freezing and melting are equal, so there is no net change in the amount of solid or liquid.
Therefore, the temperature at which a substance freezes is the same temperature at which it melts.
