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• Crude oil


  A mixture of lots of different hydrocarbons
• Fractional distillation


  Separates out different hydrocarbons by the length of their carbon chains
• Shortest hydrocarbons


  • Most flammable, make the best fuels
• Longer chain hydrocarbons


  • Thick viscous liquids, comparatively less useful
• Cracking


  Breaks down longer less useful hydrocarbons into shorter more flammable hydrocarbons
• Thermal decomposition


  Breaking down molecules by heating them
• Cracking methods


  • Catalytic cracking
  • Steam cracking
• Catalytic cracking


  Heat long chain hydrocarbons and vaporize, pass over hot powdered aluminium oxide catalyst which splits apart into two smaller hydrocarbons
• Steam cracking


  Vaporize hydrocarbons, mix with steam, heat to very high temperature which causes long hydrocarbon chains to split apart into shorter ones
• Balanced chemical equation for cracking long chain alkanes

  Long chain alkane (e.g. decane) goes to form shorter alkane (e.g. heptane) and alkene (e.g. propene)
• Number of carbons and hydrogens on each side of the equation must be the same
• Alkenes


  • More reactive than alkanes
  • Can be added together to make polymers
• Adding bromine water to a solution of alkenes

  Decolorizes the bromine water from orange to colorless
• Cracking reaction


  • Decane (C10H22) can be cracked into ethene (C2H4) and another hydrocarbon
• Balanced equation for cracking decane

  Decane (C10H22) goes to form ethene (C2H4) and another hydrocarbon (C8H18)
• Crude oil


  A fossil fuel that we get from deep under the ground, a mixture of lots of different compounds
• Crude oil


  • Nearly all of the compounds are hydrocarbons which contain only hydrogen and carbon
  • The most common type of hydrocarbons are alkanes
• Formation of crude oil

  1. Remains of dead plants and animals, particularly plankton, buried in the mud

  2. High pressures and temperatures under the ground turned this organic biomass into crude oil

  3. Crude oil soaked into the rocks and was stored for millions of years
• Crude oil is a finite resource
• Fractional distillation


  A process used to separate the different hydrocarbons in crude oil by making use of their different boiling points
• Fractional distillation


  1. Feed the oil into a chamber and heat it until most of it has turned into a gas

  2. Pass the gaseous mixture into a fractionating column which is hot at the bottom but gets cooler towards the top

  3. Hydrocarbons with the longest chains condense first and drain out early

  4. Shorter chain hydrocarbons stay gaseous longer and condense higher up the column
• Fractions obtained from fractional distillation

  • Bitumen
  • Heavy fuel oil
  • Diesel
  • Petrol
  • Kerosene
  • LPG (propane and butane)
• Fractions from fractional distillation

  • Shorter chain hydrocarbons are more flammable and make better fuels
  • Longer chain hydrocarbons are often poor fuels and can be broken down further by cracking
• Petrochemicals


  Substances obtained from crude oil that can be used as feedstock (raw materials) for the petrochemical industry to make things like solvents, lubricants, polymers and detergents
• Alkanes


  A homologous series of hydrocarbons that contain only carbons and hydrogen atoms with no double bonds
• We covered the names of the first four alkanes in the series in this video
• Alkanes


  • As the length of the carbon chain increases:
  • Boiling point increases
  • Shorter alkanes are more volatile and evaporate more easily
  • Longer alkanes are more viscous and thick
  • Shorter alkanes are more flammable and easier to ignite or burn
• Combustion reactions


  1. Hydrocarbon reacts with oxygen

  2. Forms carbon dioxide and water

  3. Releases energy (exothermic)
• Complete combustion


  Hydrocarbon reacts with enough oxygen to form carbon dioxide and water
• Writing balanced combustion equations

  1. Write unbalanced equation

  2. Balance carbon atoms

  3. Balance hydrogen atoms

  4. Balance oxygen atoms
• Hydrocarbons like alkanes are used as fuels because they release energy when combusted