The boiling point of a liquid is the temperature at which it transforms into a vapor, that is, the temperature at which its vapor pressure is equal to that of its surroundings. Therefore, the boiling point depends on the pressure of the environment of the liquid; the lower the pressure, the lower the boiling point.
There is a part of the liquid that turns into a vapor after the boiling point; these molecules are close to the surface of the liquid and escape into the environment. This phenomenon is called evaporation. In boiling, the transformation of liquid into vapor occurs in the entire volume of liquid, as can be seen in boiling water.
The normal boiling point of a liquid is the boiling temperature when the pressure of its surroundings is one atmosphere, that is, it is the normal atmospheric pressure at sea level. The normal boiling point of water is 100 degrees Celsius; while the normal boiling point of ethanol, the most used alcohol, is 78.3 degrees Celsius.
Sources
Goldberg, David. 3000 Solved problems in chemistry . McGraw-Hill Education 2011.
Haynes, William. CRC Handbook of Chemistry and Physics . CRC Press Book, 2012.
boiling point . Concept of. Editorial Edecé.
