How does chain length affect the properties of alkanes?

The length of the alkane chain affects its boiling point, melting point, viscosity, and flammability.

The properties of alkanes are significantly influenced by the length of their carbon chain. As the chain length increases, the boiling and melting points of the alkanes also increase. This is due to the fact that longer chains have more points of contact and thus stronger London dispersion forces (a type of intermolecular force). These forces require more energy to overcome, leading to higher boiling and melting points.

In addition to this, the viscosity, or resistance to flow, of alkanes also increases with chain length. Longer chains tend to tangle and resist flow more than shorter ones, making them more viscous. This is why substances like motor oil, which are made of long-chain alkanes, are much thicker and slower to flow than substances like petrol, which are made of short-chain alkanes.

The flammability of alkanes is another property that is affected by chain length. Short-chain alkanes are generally more flammable than long-chain alkanes. This is because short-chain alkanes vaporise more easily, and it is the vapour of a substance, not the liquid, that burns. Therefore, substances with shorter chains, which can vaporise at lower temperatures, are more likely to catch fire.

In summary, the length of the alkane chain has a significant impact on its physical properties. Longer chains lead to higher boiling and melting points, increased viscosity, and decreased flammability. Understanding these relationships is crucial in many areas of chemistry and industry, from the production of fuels to the design of synthetic materials.