Alkanes

Alkanes

1. Hydrocarbons from Crude Oil

   • Source of hydrocarbons
     • Separated as fractions with different boiling points- Fractional Distillation
       • Can be used as fuels, or for processing into petrochemicals
       • Different strength Van der Waals forces
         • Cause the variations in Boiling Points
         • Due to different carbon chain lengths and branching
   • Saturated Hydrocarbons
     • Single bond between C atoms
   • Have a tetrahedral shape around the carbon atom
     • Bond angles of 109.5
   • Fractional Distillation
     • 1.Crude oil is vaporised and then passed through a fractioning column, it is hotter at the bottom than at the top
     • 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. The vapor then condenses to a liquid, the liquid fractions are then tapped off into storage containers

2. Hydrocarbons as fuels

   • Catalytic Cracking
     • Uses to break larger carbon chains which have low demand into smaller chains which have a high demand
       • For example:Paraffin (decane) into petrol (octane) and ethene
     • 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
   • Environmental Issues
     • Crude oil is non-renewable
     • Problems caused by CO2 emissions from burning fossil fuels
       • Global Warming
     • Bio-diesels being produced,
       • Made from Rapeseed or Alcohol by fermenting sugars
   • Reforming
     • Aliphatic (straight chains) chains are turned into cyclic alkanes
       • This process is carried out because cyclic chains make fuel burn more efiiciently
   • Isomerisation
     • Un-branched alkanes (straight chained) are converted into branched alkanes
       • For example: Hexane- 2,3-dimethylbutane
       • This promotes efficient combustion

3. Substitution Reactions

   • Using UV radiation, by Cl2 and Br2, to form halogenoalkanes
   • Mechanism of CH4 + Cl2 CH3Cl + HCl
     • 3.Termination
       • Cl. + Cl. Cl2
       • .Cl + .CH3 CH3Cl
       • .CH3 + .CH3 C2H6
     • 2. Propogation Steps
       • CH4 + .Cl .CH3 + HCl .CH3 + Cl2 CH3Cl + .Cl
     • 1. Initiation
       • Cl2 2.Cl MUST HAVE UV LIGHT
         • This is an example of Homolytic fission