Melting and Boiling Points Class 11 Notes | EduRev

: Melting and Boiling Points Class 11 Notes | EduRev

What is Boiling Point?

The boiling point is the temperature at which the vapour pressure of the liquid is equal to the atmospheric pressure of the liquid and the liquid is converted to vapour. The boiling point of the liquid depends upon the pressure of the surrounding. When the liquid is at high pressure, it has higher boiling point than the boiling point at normal atmospheric pressure. The boiling point of different liquids is different for a given pressure. In 1982 IUPAC, defined standard boiling point which is the temperature at which liquid boils under the pressure of 1 bar. The boiling point changes with altitude and that’s why when we go to mountain areas i.e. at higher altitudes cooking food takes more time because the pressure decreases and therefore because of this it takes more time in cooking food at hilly areas.

What is Melting Point?

The temperature at which solid changes its state to liquid at an atmospheric pressure is called the melting point of that liquid. This is the point at which both liquid and solid phase exists at equilibrium. The melting point of the substance also varies with pressure and is specified at standard pressure.

Another term is freezing point which is just reverse of melting point which is the temperature at which liquid is converted to solid. Technically, you can say that melting point and freezing point are not same because a substance can be super cooled below its freezing point without forming solid.

Let us know the boiling point and melting point of different substances:

   Name of the substance         Boiling point(K)                  Melting point(K)
             Aluminium               2740                  932
              Copper               1460                  1359
              Gold               2933                   1336
            Hydrogen                20.3                   13.8
            Mercury                630                   234
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