What is the chemical formula for petrol and diesel?

Petrol (also known as gasoline) and diesel are not single compounds but rather mixtures of hydrocarbons. Therefore, they do not have a fixed chemical formula like simple molecules such as H₂O or CO₂. Instead, their composition is represented by the range of hydrocarbons they contain.

Petrol (Gasoline):

• Petrol is primarily composed of hydrocarbons in the range of C₄ to C₁₂.
• These hydrocarbons include alkanes (paraffins), cycloalkanes (naphthenes), and aromatic hydrocarbons.
• A general representation of petrol is C₈H₁₈ (octane), which is often used as a reference compound for fuel quality in terms of the octane rating.

Diesel:

• Diesel fuel is heavier and consists of hydrocarbons with carbon chains ranging from C₁₂ to C₂₀.
• These hydrocarbons are mainly alkanes and aromatic compounds.
• A commonly used approximate formula to represent diesel is C₁₂H₂₃.

Key Difference:

• Petrol is more volatile, burns faster, and is suitable for spark-ignition engines.
• Diesel is less volatile, has a higher energy density, and is used in compression-ignition engines.

In conclusion, petrol and diesel do not have a fixed formula, but they can be approximately represented as C₈H₁₈ (petrol) and C₁₂H₂₃ (diesel).