Alkanes are described as saturated hydrocarbons. Explain what this means and describe how the boiling point and flammability of alkanes change as the length of the carbon chain increases. Use your knowledge of alkane properties to explain why shorter-chain alkanes make better fuels.

Alkanes are hydrocarbons composed only of carbon and hydrogen atoms.

Saturated means that all the carbon–carbon bonds are single bonds; there are no double or triple bonds.

When the carbon chain length increases the van der Waals forces between the molecules become larger, so the boiling point rises.

With a longer chain the alkane is less flammable – shorter chains ignite more readily.

Short‑chain alkanes are better fuels because they are more flammable, they ignite more easily and their lower boiling points allow them to vapourise quickly, giving a higher rate of combustion.