Why does acetone evaporate faster than ethanol yet still has a higher surface tension?

I would expect it to have a lower surface tension... I got the data from surface-tension.de.


Surface tension and evaporation are not as linked with each other as posed by your question. They are two distinct characteristics of liquids which generally follow direct relationship but not always. There are several other factors which you should not ignore:

  • Surface tension is the inherent force of liquid described by its tendency to minimize its surface area. A liquid with high molecular attraction takes account for a higher surface tension. It's temperature dependent and does not have similar slopes for all liquids. The case you provided is for standard temperature i.e. 20 C so you may get a contrary result at some other temperature. Compare: http://www.ddbst.com/en/EED/PCP/SFT_C11.php and http://www.ddbst.com/en/EED/PCP/SFT_C4.php2.
  • Evaporation usually deals with heat capacity, thermal energy required to overcome inter-molecular attractions and other thermal properties. Usually higher surface tension means energy required to overcome inter-molecular attractions is higher hence it may also have a higher value for the liquid having higher surface tension but it is not necessary. So liquids resembling each other in thermal properties usually form intersecting surface tension curves. i.e. one have a larger value till intersecting temperature and later on second has more. Ethanol and propanone is also such borderline case to be compared.

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