Alkanes

Summary and Exam Tips for Alkanes

Alkanes is a subtopic of Organic Chemistry, which falls under the subject Chemistry in the Cambridge IGCSE curriculum. Alkanes are the simplest family of hydrocarbons, characterized by their single covalent bonds, making them saturated hydrocarbons. They follow the general formula $C_nH_{2n+2}$ and are known for being generally unreactive. However, they do participate in combustion and substitution reactions. During complete combustion, alkanes react with oxygen to produce carbon dioxide and water, releasing significant energy, which is why they are used in fuels like LPG and petrol. In substitution reactions, alkanes react with halogens in the presence of ultraviolet light, which provides the activation energy ($E_a$), resulting in the formation of halogenoalkanes. This process is a photochemical reaction. An example of such a reaction is $CH_4 + Cl_2 \rightarrow CH_3Cl + HCl$. Alkanes are crucial in everyday applications due to their energy release properties when burned.

Exam Tips

• Understand the Structure: Remember that alkanes have only single covalent bonds, making them saturated hydrocarbons. This is crucial for identifying them in structural formulas.
• Combustion Products: Be clear that complete combustion of alkanes produces carbon dioxide and water, while incomplete combustion results in carbon monoxide and water.
• Substitution Reactions: Know that alkanes undergo substitution reactions with halogens in the presence of UV light, which acts as the activation energy.
• General Formula: Familiarize yourself with the general formula $C_nH_{2n+2}$ for alkanes, as it helps in predicting the molecular structure of different alkanes.
• Practical Applications: Recognize the role of alkanes in fuels like LPG and petrol, emphasizing their importance in energy production.