- The evaporation rate is a measure of the volatility of substances, defined as the ratio of the evaporation time of a substance to that of diethyl ether under the same conditions.
- Liquids form vapors well below their boiling point and without additional heat supply, which, if they can escape, cause the volume of the liquid in the starting vessel to decrease over time. This process is known as evaporation.
- The speed at which a liquid evaporates depends on its chemical composition and numerous environmental parameters.
- If the evaporation times are determined under the same conditions (standard at 20 ° C and 65% relative humidity), only the effects due to the chemical composition remain.
- The evaporation time of the substance to be tested is now compared with that of diethyl ether as the reference substance.
- The resulting value is dimensionless and is called the evaporation number.
- The lower the evaporation rate, the faster a substance evaporates, the higher the rate, the slower.
- Due to the choice of the rapidly evaporating diethyl ether as the reference substance, almost all of the evaporation numbers are greater than 1.
- One of the few liquids that evaporates faster than diethyl ether and therefore has a lower evaporation number is n-pentane.
- The lower the evaporation rate of a flammable liquid, the greater the risk that ignitable or explosive gas mixtures are present above it.
Evaporation rates of some liquids
|Methyl ethyl ketone||6,0|