Melting Point:
This is the temperature at which a solid substance transitions into its liquid phase.
Imagine ice cubes sitting in a warm room. As the temperature rises, the ice reaches its melting point, where it starts to turn into water.
At the melting point, both the solid and liquid phases coexist in equilibrium. This means the rate of solid melting into liquid is equal to the rate of liquid solidifying back into a solid.
Boiling Point:
This is the temperature at which a liquid transforms into its gaseous (vapor) phase.
Think about water boiling in a pot. As you heat the water, it reaches its boiling point, where it vigorously transitions into steam.
The boiling point is influenced by external pressure. For instance, water boils at 100°C at standard atmospheric pressure, but boils at a lower temperature on a mountaintop due to the lower air pressure.
At the boiling point, the vapor pressure of the liquid equals the surrounding pressure. Vapor pressure is the pressure exerted by the vapor of a substance in equilibrium with its liquid phase.
Example:
Water: Melting point = 0°C, Boiling point = 100°C (at standard pressure)
Iron: Melting point = 1538°C, Boiling point = 2862°C