* Stronger Van der Waals forces: Long hydrocarbon chains have a larger surface area compared to shorter chains. This larger surface area leads to stronger London dispersion forces (a type of van der Waals force). These forces arise from temporary fluctuations in electron distribution within the molecule, creating temporary dipoles that attract neighboring molecules.

* More energy required to overcome intermolecular forces: The stronger the intermolecular forces, the more energy is required to overcome them and cause the substance to change from a liquid to a gas (boiling).

In summary: The longer the hydrocarbon chain, the stronger the van der Waals forces between the molecules, leading to a higher boiling point.