Boiling point | Applications of boiling point

The temperature at which the vapor pressure of a liquid is equal to the vapor pressure of the atmosphere or some other external pressure is called boiling point.

Example.

Boiling point of water is 100 centigrade at 760 Torr pressure.

Molar heat of vaporization.

The amount of heat is required to vaporize one mole of a liquid at its boiling point is called molar heat of vaporization.

Effects intermolecular forces on the boiling point

Ether, alcohol and water have different boiling points, but have the same vapor pressure on which they boil. It is due to the reason that ether has less intermolecular forces than alcohol and water. Similarly, alcohol has less intermolecular forces than water. The line of water in graph starts from 4.8 tour and line of Ether starts from 200 torr.

Effects of external pressure

On boiling point.

Boiling point of a liquid is directly proportional to the external pressure. If the external pressure is decreased, then the boiling point of a liquid also decreases.

Example.

At 23.7 torr pressure the water boils at 25 degrees centigrade temperature. And at 1489 torr pressure the water boils at 120 degree centigrade temperature.

What is the effect of boiling point at Murree Hills and Mount Everest?

Boiling point is increased with the increase in external pressure and vice versa. At Murree Hill, the external pressure is 700 torr and water boils at 98 degree centigrade.

Similarly, at Mount Everest the external pressure is 323 torr and water boils at 69 degree centigrade temperature.

Applications of boiling point

Vacuum distillation

The separation of a liquid at a reduced pressure is called vacuum distillation. Some liquids have high boiling points and cannot be separated from the mixture because they decompose before their boiling temperature. 

Example.

Glycerin has a 290 degree centigrade boiling point and decomposes before reaching this temperature. So if we decrease the external pressure up to 50 torr glycerin boils at 210 degree centigrade and separates easily without decomposition. 

Pressure cooking

Pressure cooking is based upon the principle that the food in the pressure cooker boils faster. Due to this reason, no vapors leave the system and vapor pressure becomes equal to the external pressure quickly.