Illustrated Glossary of Organic Chemistry

Vapor pressure: The gas pressure exerted by vapors of a substance. Boiling point is defined as the temperature at which the vapor pressure of the substance being boiled is equal to the ambient pressure (atmospheric pressure, or less, if the sample is under reduced pressure or a vacuum).

         
Menthol has a fairly high vapor pressure at room temperature, which is why it has a very noticeable, minty odor. It is because of this high vapor pressure that menthol is used as a fragrant analgesic in many over-the-counter pair relief medicines.          





The boiling point of water is 100oC at 1.0 atmosphere of pressure. At this temperature the vapor pressure of water vapor is equal to 1.0 atmosphere. At lower temperature water's vapor pressure is lower, but still high enough that it evaporates readily even at room temperature.