Alkanes

Alkanes

Hydrocarbons from Crude Oil
1. Source of hydrocarbons
  1. Separated as fractions with different boiling points- Fractional Distillation
    1. Can be used as fuels, or for processing into petrochemicals
    2. Different strength Van der Waals forces
      1. Cause the variations in Boiling Points
      2. Due to different carbon chain lengths and branching
2. Saturated Hydrocarbons
  1. Single bond between C atoms
3. Have a tetrahedral shape around the carbon atom
  1. Bond angles of 109.5
4. Fractional Distillation
  1. 1.Crude oil is vaporised and then passed through a fractioning column, it is hotter at the bottom than at the top
  2. 2.The gases then pass up through the column through a series of bubble caps, they eventually reach a temperature that is lower than their boiling point
  3. 3. The vapor then condenses to a liquid, the liquid fractions are then tapped off into storage containers
Hydrocarbons as fuels
1. Catalytic Cracking
  1. Uses to break larger carbon chains which have low demand into smaller chains which have a high demand
    1. For example:Paraffin (decane) into petrol (octane) and ethene
  2. It is carried out by heating the large hydrocarbon, with a porcelein catalyst, the vapor produced then condenses into a smaller hydrocarbon (alkane) and an alkene
2. Environmental Issues
  1. Crude oil is non-renewable
  2. Problems caused by CO2 emissions from burning fossil fuels
    1. Global Warming
  3. Bio-diesels being produced,
    1. Made from Rapeseed or Alcohol by fermenting sugars
3. Reforming
  1. Aliphatic (straight chains) chains are turned into cyclic alkanes
    2. This process is carried out because cyclic chains make fuel burn more efiiciently
4. Isomerisation
  1. Un-branched alkanes (straight chained) are converted into branched alkanes
    1. For example: Hexane- 2,3-dimethylbutane
    2. This promotes efficient combustion
Substitution Reactions
1. Using UV radiation, by Cl2 and Br2, to form halogenoalkanes
2. Mechanism of CH4 + Cl2 CH3Cl + HCl
  1. 3.Termination
    1. Cl. + Cl. Cl2
    2. .Cl + .CH3 CH3Cl
    3. .CH3 + .CH3 C2H6
  2. 2. Propogation Steps
    1. CH4 + .Cl .CH3 + HCl .CH3 + Cl2 CH3Cl + .Cl
  3. 1. Initiation
    1. Cl2 2.Cl MUST HAVE UV LIGHT
      1. This is an example of Homolytic fission

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