Changes in State

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.


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