Eli5 Why does oil not evaporate like water?



Eli5 Why does oil not evaporate like water?

In: Chemistry

Oil has a much higher boiling point. That basically means it’s molecules need a lot more energy before they can convert to a gas.

Water boils at 100C.

Oil, depending on the type & purity, is more like 200-300C.

As a result, at the same temperature, a lot more water molecules will be going fast enough to escape than oil molecules. This means the water evaporates *much* faster. The oil still is evaporating, it’s just so slow at room temperature that you don’t notice it much.

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”.