# Why is the boiling point of a solution higher than that of a pure solvent? [duplicate]

Why is the boiling point of a solution higher than that of a pure solvent?
I think when a non-volatile solid solute is added to a solvent, some of the liquid solvent molecules are replaced by solute molecules at the surface. The lesser the number of solvent molecules at the surface that fewer molecules evaporate, and thus the vapor pressure of the solution will be lower than the pure solvent.

Is this correct?

• Can a solute affect the entropy of the system? Google colligative properties.
– user5764
Commented Jul 7, 2016 at 15:57
• The change in vapour pressure with added solute is called Raoults law. Other colligative properties are elevation of boiling point, depression of freezing point and Osmotic pressure. These depend only on the number of solute molecules in a fixed volume of solvent, not their nature. Commented Jul 7, 2016 at 19:17
The change in vapour pressure with added solute is called Raoults law. The vapour pressure of a species i above a solution is proportional to mole fraction of this species (solute) $x_i$ and its pure vapour pressure $p_i^*$ or $p_i=x_i.p_i^*$.