III). Changes in State:
Solid to Liquid: Melting
Liquid to Solid: Freezing
Liquid to Gas: Evaporation or Boiling
Gas to Liquid: Condensation
Solid to Gas: Sublimation
Gas to Solid: Solidification
Melting and boiling points are important in identifying a substance and testing its purity. Pure substances have definite melting and boiling points. The presence of impurities will cause boiling points to rise and melting points to fall.
- The constant temperature at which a pure solid changes into a liquid is called its melting point.
- The constant temperature at which a pure liquid changes into a gas is called its boiling point.
Heating curve of a pure substance:
Cooling curve of a pure substance:
Note: the parts in both graphs that do not show any temperature change are the parts in which the state changes occur. In them, both states occur together.