Name: Rzvana F.
Does oil evaporate? Why?
When a liquid evaporates, its molecules must separate themselves from their attachment with
others in the liquid and then move off into the air space above. Heating the liquid makes the
molecules move faster and weakens their attachment to each other. That is why warm liquids may
evaporate more quickly than if they were cold.
Nevertheless, the molecules in some kinds of liquids, like oil for example, are rather large and
well-tangled up and attached to each other. This means that evaporation, if it occurs at all, is
very slow. That is why cooking oil, even though sometimes heated to a very high temperature,
does not evaporate to an appreciable extent.
Let us define 1 'mole' of Chemical X the same as 602,000,000,000,000,000,000,000 molecules of
Chemical X. This is also
called Avogadro's number. For example, one 'mole' of methane, for example, is the same as
602, 000, 000, 000, 000, 000, 000, 000 molecules of methane.
YES. Oil does evaporate. But it evaporates in a weird way. Oil is not a pure compound. Oil
is a blend of many different sizes of what chemists call 'hydrocarbons' or 'molecules'. These
molecules range from very very small (16 grams / mole ) to very very large molecules
(100s-1,000s of grams / mole)
The lighter molecules will evaporate quicker than the heavier molecules. WHY?
Let us pretend there is an oil called Rzvana's Blend. It is made of only 10 different
Molecule 1 weighs about 16 g / mole.
Molecule 2 weighs about 32 g / mole.
Molecule 10 weighs about 160 g / mole.
If you want to understand how oil evaporates you need to know how evaporation really works.
Evaporation happens when a molecule has enough energy to leave its fellow liquid molecules
surrounding it. For any given temperature, or energy, the smaller molecules will move quicker
than the larger molecules. Think about kicking a soccer ball versus kicking a bowling ball. OF
COURSE I DO NOT RECOMMEND KICKING A BOWLING BALL. However, if you imagined it, the soccer ball
will travel much faster than the bowling ball. This is what happens in oil. The temperature is
the energy from your "foot" and the 10 balls that have 10 different masses are the molecules in
the oil. Now you can imagine that over a long period of time the lighter molecules will tend to
evaporate away leaving the larger and heavier molecules behind.
If this does not completely answer your question, or if my explanation was a little fuzzy please
feel free to email us back.
But I hope this helps.
"Oil" can be a lot of different things. It could be the "stuff" you put into a car's engine. It
could be what you cook with. It could be what you put on a bicycle chain. Many liquids and
solids have a certain amount that is also present as a gas or vapor. Water is an example. The
amount of the gas or vapor depends upon what the chemical makeup of the liquid or solid is, and
upon the temperature. Again, using water as an example, at the boiling point there is a lot of
water present as a gas, so it evaporates
fast, but at the freezing point there is much less water present as a vapor or gas so ice (solid
water) does not evaporate very quickly. Most things that we think of as being oils do not have
very much of the liquid present as a gas, so they do not usually evaporate quickly at room
temperature. However, if the oil is heated to high enough temperature it can evaporate too.
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Update: June 2012