Alkanes, Alkenes, alcohol and plastics

• 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
• 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
• C2H4 + H2 → C2H6
• 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
• C2H4 + Br2 → C2H4Br2
• Properties of plastics


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