Crude oil and fuels

• Combustion of hydrocarbons


  1. Requires oxygen (from the air)

  2. Burning hydrocarbons produces carbon dioxide and water
• Methane + oxygen


  CH4 + O2 → CO2 + H2O
• All combustion reactions are exothermic, i.e. they release heat
• Hydrogen as a fuel

  • Used as a rocket fuel and in hydrogen fuel cells
  • Produced from water, therefore renewable
  • Water is the only product of its combustion so burning hydrogen does not contribute towards global warming or acid rain
  • Ignites easily
  • Forms an explosive mixture with air
• Disadvantages of hydrogen as a fuel

  • Requires large amounts of electricity to produce hydrogen from water by electrolysis
  • Storage requires bulky and heavy pressurised containers
• Ethanol as a fuel

  • An example of a biofuel made from crops such as corn, sugar cane and rapeseed
  • Can be mixed with petrol and used as a fuel in cars
• Advantages of ethanol as a fuel

  • Renewable
  • Carbon-neutral, i.e. the amount of carbon dioxide absorbed by plants during photosynthesis balances the amount of carbon dioxide released on burning the fuel made from them
• Disadvantages of ethanol as a fuel

  • Dependent on climate for sugar growth
  • Decreases the amount of land available to grow food crops - could result in higher food prices
• Fire triangle


  • Shows the factors required for combustion to occur
  • Firefighting and fire prevention are based on removing one or more factors
• Removing factors from the fire triangle

  • Carbon dioxide and fire blankets can be used to remove oxygen
  • Water can be used to remove heat
  • Trees can be felled to remove fuel in a forest fire
• Hydrocarbons


  • Compounds that contain carbon and hydrogen atoms only
  • Carbon atoms have the ability to form bonds with other carbon atoms resulting in the formation of hydrocarbon chains
  • Longer chains have higher boiling points
• Crude oil


  • A complex mixture of hydrocarbons, which can be separated by fractional distillation
  • Produced from the remains of dead marine animals and plants that lived around 300 million years ago
  • Layer upon layer of sediments built up over time and pressure and heat caused the remains to break down, forming crude oil
• Fractional distillation


  1. Crude oil is boiled/vaporised before it enters the fractionating column

  2. Hydrocarbons condense at different heights in the column

  3. The lower the boiling point, the higher in the column a compound is collected

  4. Fractions are mixtures containing hydrocarbon compounds that have similar chain lengths and, therefore, similar boiling points
• Intermolecular forces


  • Larger hydrocarbon molecules have more intermolecular forces, and so more energy is needed to overcome them in order for melting or boiling to occur
  • Longer chain hydrocarbons are more viscous (i.e. thicker liquids, less easy to pour)
• Fractions from fractional distillation of crude oil

  • Refinery gases
  • Petrol
  • Naptha
  • Paraffin (kerosine)
  • Diesel oil (gas oil)
  • Lubricating oil
  • Bitumen
• HEAT, FUEL, OXYGEN are the three factors required for combustion to occur