Answer to Question #340288 in General Chemistry for denden

Question

Gasoline contains hydrocarbon such as octane, C8H18. Motor oils contain much larger molecules such as C18H38. Which is more viscous liquid? Explain why.

Answer 1

Because its molecules can slide around each other, a liquid has the ability to flow. The resistance to such flow is called the viscosity.

Viscosity is governed by the strength of intermolecular forces and especially by the shapes of the molecules of a liquid. Liquids whose molecules are polar or can form hydrogen bonds are usually more viscous than similar nonpolar substances.

Liquids containing long molecules are invariably very viscous. This is because the molecular chains get tangled up in each other like spaghetti—in order for the liquid to flow, the molecules must first unravel.

So Motor oils are more viscose, because their molecules are larger then gasoline.