7.1.3 Properties of Hydrocarbons

Hydrocarbons exhibit various properties that depend on the size of their molecules. These properties play a significant role in determining how hydrocarbons are used as fuels. Some key properties include boiling point, viscosity, and flammability.

• Boiling point: The boiling point of a hydrocarbon generally increases with increasing molecular size. Larger hydrocarbon molecules have stronger intermolecular forces of attraction, which require more energy to break and convert the substance from a liquid to a gas. As a result, larger hydrocarbons have higher boiling points compared to smaller ones.
• Viscosity: Viscosity refers to the resistance of a liquid to flow. In hydrocarbons, viscosity also tends to increase with increasing molecular size. Larger hydrocarbon molecules have more complex molecular structures and exhibit stronger intermolecular forces, leading to higher viscosity. This means that larger hydrocarbons flow less easily than smaller ones.
• Flammability: Hydrocarbons are highly flammable due to their carbon and hydrogen content. The flammability of hydrocarbons generally increases with decreasing molecular size. Smaller hydrocarbons have simpler molecular structures and can vaporise more readily, allowing for faster combustion. Larger hydrocarbons require more energy to vaporise and may have a slower rate of combustion.

The combustion of hydrocarbon fuels involves the reaction of carbon and hydrogen with oxygen, resulting in the release of energy. During complete combustion, hydrocarbons combine with oxygen to produce carbon dioxide (CO₂) and water (H₂O). The balanced equation for the complete combustion of a hydrocarbon can be written by ensuring that the number of atoms of each element is the same on both sides of the equation.