Eli5 Why does oil not evaporate like water?
In: Chemistry
In a way, it’s because if an oil does evaporate, we decide not to call it an oil.
Oil molecules are mostly chains of carbon atoms with hydrogen stuck to them. A lot of oil molecules, like those in heating fuel oil or lubricating oil, are long chains. Because they are long it takes a lot of energy to get them to leave their liquid state and fly around like a gas.
There are smaller chains of carbon: pentane, hexane, heptane, and octane, for example, are found in gasoline. They are fairly small, but fundamentally no different from the larger molecules in what we call oil. Because they are smaller, they do evaporate like water. We just choose not to call gasoline “oil”.
You can go even smaller. Methane, ethane, propane, and butane are even smaller chains, again fundamentally the same as oil. Because they are so small, are gases at room temperature – they have already evaporated before we get a chance to do anything. Again, we just choose to not call these things “oil”.
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