How does the boiling point of alkanes typically change with increasing relative mass?

The boiling point of alkanes generally increases with increasing relative mass due to the larger molecular size and surface area associated with heavier alkanes. As the chain length of the alkane increases, the number of carbon and hydrogen atoms increases, leading to a greater molecular weight. This increase in size results in stronger van der Waals (dispersion) forces between the molecules because of an increased surface area for interactions.

These dispersion forces require more energy to overcome when transitioning from liquid to gas, which in turn raises the boiling point of the alkane. So as alkanes increase in mass with more carbon atoms, their boiling points rise systematically. This trend can be observed in the alkane series, where for example, methane has a much lower boiling point compared to pentane, which is higher, and this pattern continues with larger alkanes.