Impurities in the solution increase the boiling point. This is because impurities decrease the water molecules available for vaporisation during boiling. A greater amount of heat is needed to make the same amount of impure solution to vapourize than the heat that is required to make a pure solution vaporize.

In fact, as the boiling point of a solvent increases, its freezing point decreases. An example of this would be the addition of salt to an icy sidewalk. The solute (salt) reduces the freezing point of the ice, which allows the ice to melt at a lower temperature. ​.

But we can’t use salt as an antifreeze in mechanical cooling systems because of a few limiting factors. In addition to dissolving in water — which salt does quite admirably — a useful antifreeze needs to remain chemically inert, meaning that it doesn’t interact with the surfaces of the system.

Atmospheric Pressure and Boiling The pressure of gas above a liquid affects the boiling point. In an open system this is called atmospheric pressure. The greater the pressure, the more energy required for liquids to boil, and the higher the boiling point.

The boiling point of a liquid varies according to the applied pressure; the normal boiling point is the temperature at which the vapour pressure is equal to the standard sea-level atmospheric pressure (760 mm [29.92 inches] of mercury). At sea level, water boils at 100° C (212° F).

In the liquid state, the forces of interaction are less and therefore, water exists as a liquid at room temperature. The boiling point of water is 100 °C, i.e. the vapour pressure of water becomes equal to atmospheric pressure at 100 °C at sea level.

If a liquid is heated the particles are given more energy and move faster and faster expanding the liquid. The most energetic particles at the surface escape from the surface of the liquid as a vapour as it gets warmer. Liquids evaporate faster as they heat up and more particles have enough energy to break away.