Change of State (Boiling, Melting) A phase transition is a change in the physical state of a substance where its properties change discontinuously. There ar...
Change of State (Boiling, Melting)
A phase transition is a change in the physical state of a substance where its properties change discontinuously. There are two main phase transitions: boiling and melting.
Boiling
During boiling, a liquid turns into a gas (vapor) and the temperature of the substance rises. This is an endothermic process, meaning that energy is absorbed from the surroundings. The boiling point is the temperature at which the vapor pressure of the liquid is equal to the atmospheric pressure. At the boiling point, the pressure of the gas is equal to the atmospheric pressure, and the liquid is said to be saturated.
Melting
On the other hand, during melting, a solid turns into a liquid. This is an exothermic process, meaning that energy is released to the surroundings. The melting point is the temperature at which the heat energy required to melt the solid is equal to the heat energy released when the solid turns into a liquid. Above the melting point, the solid is said to be unsaturated, meaning that there is more solid present than there is vapor.
Examples
When you boil water, the water temperature rises, and the water turns into a gas (steam).
When you melt ice, the ice temperature rises, and the ice turns into a liquid (water).
When you heat a metal, the metal turns from a solid to a liquid (melting).
When you cool a liquid, the liquid turns from a gas to a solid (condensation)