Crude Oil & Fuels

Crude oil plays a vital role in modern life, and understanding its chemistry is essential for GCSE Chemistry. This topic explores what crude oil is made of, how it's processed, and why it’s so important to everyday life.

What is Crude Oil?

Crude oil is a fossil fuel formed from the remains of ancient marine organisms, buried under layers of rock for millions of years. It’s a mixture of hydrocarbons — compounds made up only of hydrogen and carbon atoms.

Hydrocarbons and Alkanes

The hydrocarbons found in crude oil come in many shapes and sizes. One key type is the alkanes, which are saturated hydrocarbons. This means they only contain single bonds between carbon atoms.

General formula for alkanes:

Examples include:

• Methane (CH₄)
• Ethane (C₂H₆)
• Propane (C₃H₈)

As you go up the series, the boiling point increases and the flammability decreases.

Complete Combustion of Hydrocarbons

When alkanes burn in plenty of oxygen, they undergo complete combustion, producing:

• Carbon dioxide (CO₂)
• Water (H₂O)
• And releasing energy as heat and light

Equation Example:

This is an exothermic reaction — it gives out energy.

Fractional Distillation of Crude Oil

Crude oil is separated into useful substances using fractional distillation. This method works because hydrocarbons have different boiling points.

The crude oil is:

1. Heated until it vaporises.
2. The vapour enters a fractionating column which is hotter at the bottom and cooler at the top.
3. Different hydrocarbons condense at different heights depending on their boiling points.

Fractions include:

• Refinery gases (used for cooking)
• Petrol (car fuel)
• Kerosene (jet fuel)
• Diesel, fuel oil, and bitumen

Uses of Crude Oil

Crude oil is used to make:

• Fuels: petrol, diesel, kerosene
• Plastics and polymers
• Lubricants and solvents

It’s also the raw material for many chemicals used in medicine, agriculture, and manufacturing.

Cracking Crude Oil

Not all hydrocarbons from crude oil are equally useful. Long-chain hydrocarbons are less flammable and harder to vaporise. These are broken down in a process called cracking.

There are two main types:

• Thermal cracking (high temperature and pressure)
• Catalytic cracking (using a catalyst)

Cracking produces:

• Shorter alkanes (useful as fuels)
• Alkenes (used to make plastics)

Example Reaction:​

This helps meet demand for fuels and makes raw materials for new products.

Also see Organic Reactions, Polymers, Chemical Analysis 

Links for Learning

BBC Bitesize - Crude oil, hydrocarbons & alkanes
Study Mind - Formation of crude oil
MME - Crude oil
Study Rocket - Hydrocarbons and crude oil
Revise Chemistry - Crude oil & fractional distillation
Revision Science - Hydrocarbons from oil