Using Fuels & Fractions (AQA GCSE Combined Science: Synergy: Physical Sciences): Revision Note

Fuels and petrochemicals

Uses of petrochemicals

• The petrochemical industry is hugely important for modern society and development

• The fuels that are used in most modern methods of transport (cars, trains, airplanes, etc.) are all based on oil products

• Other useful products obtained from crude oil include:

  • Polymers

  • Lubricants

  • Solvents

  • Detergents

  • Adhesives

• The main fractions and their uses are described in the following table:

Combustion of hydrocarbons

• Hydrocarbons undergo combustion in the presence of air

  • When they undergo combustion, they release energy

Complete combustion

• Complete combustion occurs in a plentiful supply of oxygen

• The porducts of complete combustion are water and carbon dioxide gas

hydrocarbon + oxygen → carbon dioxide + water

• Carbon and hydrogen from the fuel are oxidised / gain oxygen: 

  • Hydrogen oxidises to form water

  • Carbon oxidises to form carbon dioxide

• For example, the simplest alkane, methane burns as follows:

CH₄ +  2O₂ → CO₂ +  2H₂O

• Petrol is largely composed of isomers of octane, C₈H₁₈ , which requires large amounts of oxygen to combust fully

2C₈H₁₈ + 25O₂ → 16CO₂ + 18H₂O

• The efficiency of car engines does not usually enable all the petrol to burn

  • So, car exhaust fumes contain small amounts of unburnt hydrocarbons and other products such as carbon monoxide and soot which lead to environmental problems

• The carbon dioxide produced is a major contributor to global warming and the replacement of combustion engines with electric vehicles is a major ongoing challenge for all countries