What happens to the viscosity of hydrocarbons as their molecular size increases?

As the molecular size of hydrocarbons increases, the viscosity of the hydrocarbons also increases. This is because larger hydrocarbon molecules have more atoms, leading to longer molecular chains. The increased length and mass of these molecules result in greater intermolecular forces, specifically van der Waals forces, which makes it more difficult for the molecules to slide past one another.

As hydrocarbons become larger, they also tend to be more tangled and chaotic when compared to smaller molecules, thereby resisting flow to a greater extent. This contributes to a thicker, more viscous substance. In contrast, smaller hydrocarbons tend to be less viscous because they can move more freely due to weaker intermolecular interactions. Hence, as the molecular size increases, viscosity rises accordingly.