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Name: Rzvana F.
Status: student
Age: 9
Location: N/A
Country: N/A
Date: 4/24/2003


Question:
Does oil evaporate? Why?


Replies:
Rzvana,

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.

Regards,
ProfHoff 652


Rzvana,

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 molecules:

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.

Darin Wagner


"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.

Vince Calder



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