Question
Thu April 14, 2011 By: Sarthak Kathuria

hello sir, i have a query. what is the scientific reason {on the molecular level} for the elevation of boiling point?

Expert Reply
Thu April 14, 2011
Boiling-point elevation is a colligative property. This states that a solution will have a higher boiling point than that of a pure solvent.
What is boiling ----The molecules within a liquid interact with one another with various attractive forces. These forces may include hydrogen bonds and dipole-dipole attractions.
The boiling point represents the temperature at which the liquid molecules possess enough heat energy to overcome the various intermolecular attractions that bind the molecules into the liquid. Therefore the boiling point is also an indicator of the strength of these attractive forces.
When a solute is added to a solvent, the vapor pressure of the solvent (above the resulting solution) is less than the vapor pressure above the pure solvent. The boiling point of a solution, then, will be greater than the boiling point of the pure solvent because the solution (which has alower vapor pressure)will need to be heated to a higher temperature in order for the vapor pressure to become equal to the external pressure (i.e., the boiling point).
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