Hydrocarbons
Hydrocarbons are compounds made up of only hydrogen and carbon atoms. They are the main components of crude oil and are used as fuels and feedstocks in the chemical industry.
What is a hydrocarbon?
- A hydrocarbon contains only carbon and hydrogen atoms
- The carbon atoms are joined together in chains or rings
- The simplest hydrocarbon is methane (CH₄)
Crude oil and hydrocarbons
- Crude oil is a fossil fuel, formed over millions of years from dead marine organisms
- It is a mixture of hydrocarbons
- Crude oil is separated into useful parts by fractional distillation
Types of hydrocarbons
1. Alkanes (saturated hydrocarbons)
- Only single bonds between carbon atoms
- General formula: CₙH₂ₙ₊₂
- Saturated = contain the maximum number of hydrogen atoms
Examples:
- Methane (CH₄)
- Ethane (C₂H₆)
- Propane (C₃H₈)
- Butane (C₄H₁₀)
Properties of hydrocarbons
The shorter the hydrocarbon, the:
- Lower the boiling point
- Higher the flammability
- More runny (lower viscosity)
- Cleaner it burns
Chain Length | Boiling Point | Viscosity | Flammability |
Short | Low | Low (runny) | High (easy to burn) |
Long | High | High (thick) | Low (harder to burn) |
Complete combustion of hydrocarbons
When hydrocarbons burn in excess oxygen, they produce:
- Carbon dioxide (CO₂)
- Water (H₂O)
- Lots of energy
Example:
CH₄ + 2O₂ → CO₂ + 2H₂O
💡 Complete combustion = clean blue flame
Questions
- What two elements make up a hydrocarbon?
- What is the general formula for alkanes?
- Which burns more easily – short or long hydrocarbons?
- What are the products of complete combustion?
- What is the simplest hydrocarbon?
Summary
- Hydrocarbons contain only hydrogen and carbon atoms
- Crude oil is a mixture of hydrocarbons used as fuels and feedstocks
- Alkanes are saturated hydrocarbons with only single bonds
- Shorter hydrocarbons burn more easily and have lower boiling points
- Complete combustion of hydrocarbons produces CO₂ and water