Melting Point
Definition and meaning of Melting Point in chemistry.
Melting point is the exact temperature at which a solid substance transitions into a liquid state under a specified external pressure.
In more detail
At this specific temperature, the solid and liquid phases of the substance exist in a state of thermodynamic equilibrium. Applying additional thermal energy to the system will convert more of the solid phase into the liquid phase without raising the overall temperature until the entire solid portion has completely melted. The melting point is a characteristic physical property of a pure substance and is heavily utilized in analytical laboratories to identify unknown compounds or assess their purity. The presence of impurities typically lowers the melting point and broadens the temperature range over which melting occurs.
Key facts
| Field | Physical Chemistry |
|---|---|
| Phase Transition | Solid to liquid |
| Effect of Impurities | Lowers and broadens the melting temperature range |
The normal melting point of pure crystalline water ice (H2O) is exactly 0 degrees Celsius at a standard atmospheric pressure of 1 atm.
Frequently asked questions
What happens to the substance's temperature during the melting process?
The temperature remains completely constant at the melting point until the entire solid lattice has broken down into a liquid.
How does atmospheric pressure affect the melting point?
For most common substances, increasing the external pressure slightly raises the melting point, but water is a notable exception where increased pressure actually lowers it.