Nonvolatile means that the solute itself has little tendency to evaporate. Because some of the surface is now occupied by solute particles, there is less room for solvent molecules. This results in less solvent being able to evaporate.

When a solution contains a non-volatile solute?

A solution containing non-volatile solute has higher boiling point than pure solvent, as the non-volatile solute decreases the vapour pressure of the solvent according to Raoult's law. Hence higher boiling point increases.

What happens when a non-volatile solute is added to a solvent?

The vapor pressure of a solvent is lowered by the addition of a non-volatile solute to form a solution. ... This decrease in vapor pressure can be explained by using the entropy differences of the liquid and gas phases along with the position of dissolved particles after the addition of the solute.