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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?

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  • $\begingroup$ 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. $\endgroup$
    – Poutnik
    Jan 1, 2021 at 10:57
  • $\begingroup$ 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. $\endgroup$
    – Poutnik
    Jan 1, 2021 at 11:11

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Evaporation rates are used to compare solvents for different reasons and under various conditions. One condition would be under vacuum in a rotary evaporator, to remove a low-boiling solvent to assist crystallization of a solute. Another condition would be in a paint, where you desire a higher boiler to allow enough time to spread the paint without brush strokes.

A practical way to compare evaporation rates of solvents is to put a small amount into a dish and weigh it as it evaporates. Pure compounds will have a fairly sharp disappearance and therefore a sharp time to evaporate; mixtures like kerosene or gasoline will evaporate fast at first, then slower and slower. This time, or the rate for 90% evaporation, can be compared with another solvent under the same conditions.

Evaporation rate is a commonly listed on Safety Data Sheets, and in other tables, generally compared to butyl acetate or ether. One table is at https://www.dispersetech.com/content/11-properties-of-common-solvents.

Many tables of solvent characteristics do not include evaporation rate, but do show vapor pressure at room temperature, e.g., https://sites.google.com/site/miller00828/in/solvent-polarity-table. Vapor pressure at some temperature can be a good indicator of evaporation rate, but a very strong factor in evaporation is wind, or blowing across the solvent surface. Water is particularly complicated because of relative humidity, but it and wind and temperature have been investigated for reservoirs: https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97WR02405.

Chemical distributors often list all the properties of all the solvents they deal with - and sometimes of materials they don't deal with.

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  • $\begingroup$ In that table, it is surprising that kerosene has a very low evaporation rate compare to most of the solvents (even water). $\endgroup$
    – Apurvium
    Jan 2, 2021 at 15:56
  • $\begingroup$ @Apurvium: Kerosene has a mixture of components, with mostly 10-16 carbons. It is distilled from petroleum over the range from 150 to 275C. en.wikipedia.org/wiki/Kerosene That's why it is sometimes more useful to specify an evaporation of 90% so that a difference in % of high boilers doesn't give a totally different impression of volatility. $\endgroup$
    – James Gaidis
    Jan 3, 2021 at 14:31

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