MadSci Network: Chemistry

Re: Why some liquids evaporate faster than others?

Date: Sun Nov 6 00:44:44 2005
Posted By: David Perkins, Post-doc/Fellow, Chemistry, QUT
Area of science: Chemistry
ID: 1130866713.Ch

Dear Aleksander, what a good question.

When a liquid evaporates, some of its molecules are escaping into the air as a gas. To do this, thise molecules need a certain amount of energy. The energy is different for different molecules.

Let me explain. You would agree with me that it is easier to juggle tennis balls than bowling balls, right? Well that's because bowling balls have more mass (they are heavier) and are more difficult to keep in the air. One of the factors affecting evaporation of a liquid is the mass of the molecules of the liquid. Oils are made up of enormous molecules and need a lot of energy to get into the gas phase.

Another factor affecting evaporation rates of liquids is how well the molecules are stuck together. Molecules that have a strong attraction to other moleculs in the same liquid are harder to evaporate. It's like trying to juggles a whole bunch of tennis balls that are all stuck together - water is a good example of this kind of liquid. [Molecules of H2O can form hydogen bonds among themselves.]

Also the same liquid that is kept at a different temperature or pressure will then have a different rate of evaporation. So you should conduct all of your experiments at the same temperature and pressure. I hope this helps.

Good luck with your quest.

Which of your experimental liquids do you think will evaporate the fastest?

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