# Comparison of evaporation rate of liquids

Evaporation: Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. When a molecule near the surface absorbs enough energy to overcome the vapour pressure, it will escape and enter the surrounding air as a gas.

Boiling point: The boiling point of a substance is the temperature at which the vapour pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapour.

Volatility: Volatility is a material quality which describes how readily a substance vapourizes.

Flash Point: The flash point of a volatile material is the lowest temperature at which its vapours ignite if given an ignition source.

Autoignition temperature: The autoignition temperature or kindling point of a substance is the lowest temperature in which it spontaneously ignites in a normal atmosphere without an external source of ignition, such as a flame or spark.

Fire point: The fire point of a fuel is the lowest temperature at which the vapour of that fuel will continue to burn for at least five seconds after ignition by an open flame of standard dimension.

Smoke point: The smoke point, also referred to as the burning point, is the temperature at which an oil or fat begins to produce a continuous bluish smoke that becomes clearly visible, dependent upon specific and defined conditions.

How can we compare the evaporation rate for water, alcohol, petrol and kerosene oil?

If we consider intermolecular forces as the criterion, then the order of evaporation would be:

water < alcohol < kerosene oil < petrol

But part of intermolecular forces still act in vapour phase...

What should be the criteria to compare evaporation rate of liquids at a given temperature?

• Consider room temperature saturated partial pressure in the first place, but also molar mass, diffusion coefficients, density and specific heat capacity. Both thermodynamic and kinetic properties play role. Commented Jan 1, 2021 at 10:57
• Consider also molar enthalpy of evaporation, as for the same boiling point, liquid with the higher molar enthalpy of evaporation has lower room temperature saturated partial pressure. Commented Jan 1, 2021 at 11:11