Alkanes, alkenes and crude oil

• Cracking hydrocarbons


  1. Breaking large hydrocarbons into smaller ones by heating heavier fractions to a high temperature in the presence of a catalyst

  2. An alkene is also formed
• There is greater demand for the smaller hydrocarbons and alkenes, such as ethene, are the starting material for the production of many plastics
• Alcohols


  Contain the functional group —OH, which is responsible for their properties
• Names of alcohols


  End with '-ol'
• Ethanol production by fermentation


  1. Yeast contains an enzyme which breaks down sugar, making ethanol and carbon dioxide

  2. Needs to happen in anaerobic conditions (when deprived of oxygen)

  3. Needs to happen at about 35°C
• C6H12O6 → 2C2H5OH + 2CO2
• Binge drinking and misuse of alcohol over a long period


  Social and health problems associated with it
• Sale of alcoholic drinks


  Generates significant revenue for the government
• Alcohol abuse


  Significant amount of public money spent each year in treating alcohol-related illnesses and in dealing with various other issues
• Monomers


  Small, reactive molecules that can be joined together to make a polymer
• Reactivity of a monomer


  Arises from the presence of its double bond
• Polymerisation


  One of the bonds breaks to allow the molecule to join to another
• Alkanes


  Contain single bonds between the carbon atoms only and are said to be saturated
• Names of alkanes


  End with '-ane'
• Alkenes


  Contain a double covalent bond between two carbon atoms and are said to be unsaturated
• Names of alkenes


  End with '-ene'
• Alkenes


  • ethene (C2H4)
  • propene (C3H6)
• Isomers


  Molecules which have the same molecular formula but different structures
• Isomers of C4H10


  • butane
  • methylpropane
• Addition reactions


  1. Two atoms can be added across the C=C bond in an unsaturated compound thus forming a saturated compound

  2. One atom is added to each of the carbon atoms involved
• When hydrogen is added to an alkene (hydrogenation), the corresponding alkane is formed
• Combustion of hydrocarbons


  1. Requires oxygen (from the air)

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


  Produces carbon dioxide and water
• C2H4 + H2 → C2H6
• All combustion reactions are exothermic, i.e. they release heat
• Bromine water is used in the test for alkenes as it is safer and easier to handle than bromine. It turns from orange/brown to colourless when added to an alkene
• Hydrogen as a fuel

  • Used as a rocket fuel and in hydrogen fuel cells to power cars
  • 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
• C2H4 + Br2 → C2H4Br2
• 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
  • Dependent on climate for sugar growth
  • Decreases the amount of land available to grow food crops - could result in higher food prices
• Properties of plastics


  • Good thermal and electrical insulators
  • Resistant to corrosion
  • Low density
  • Do not rot
  • Flexible
  • Strong
• Fire triangle


  Factors required for combustion to occur
• Firefighting and fire prevention


  1. Removing one or more factors from the fire triangle

  2. Carbon dioxide and fire blankets can be used to remove oxygen

  3. Water can be used to remove heat

  4. 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 the chain, the higher the boiling point
• Crude oil


  • Complex mixture of hydrocarbons
  • Produced from the remains of dead marine animals and plants that lived around 300 million years ago
  • Covered by sand and other sediments over time, 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. 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 molecules have more intermolecular forces, and so more energy is needed to overcome them in order for melting or boiling to occur
  • Explain why longer chain hydrocarbons are more viscous (i.e. thicker liquids, less easy to pour)
• Fractions from fractional distillation

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