Alkanes and Alkenes

Alkenes
1. CnH(2n)
2. At least one C=C double bond
3. Much more reactive than alkanes
4. Alkenes decolourise Bromine water
  1. This forms dibromoalkanes which are colourless
5. Combust with a sootier flame than alkanes
  1. Higher C to H ratio
  2. Combusts to form water and Carbon dioxide or water and Carbon monoxide
    1. If there is insufficient Oxygen available then incomplete combustion occurs
6. More reactive than Alkanes
  1. The C=C double bond can be split
7. One of the end products in cracking
8. Halogens can be added across the double bond
  1. Colourless di(halogen)alkanes are then formed
9. Alkenes are much too valuable to be used as a fuel
  1. It is instead used to make alcohols and polymers for plastic
Alkanes
1. Family of hydrocarbons in a homologous series
  1. A homologous series is a series of compounds with the same general formula
2. CnH(2n+2)
  1. Meth, eth, prop, but, pen, hex, hept etc.
3. Saturated hydrocarbons
  1. Carbon atoms are joined together by only single bonds
    1. Hydrocarbons can occur as...
      1. Chains
      2. Branched chains
      3. Rings
      4. A combination of these
  2. Not highly reactive
4. Alkanes with <5 Carbon atoms are gas
  1. 5-12 Carbon atoms are liquid
    1. >12 Carbon atoms are solid
  2. As the number of Carbon atoms rises, it becomes more viscous
    1. The melting point and boiling point rise
      1. It becomes less volatile
        It becomes less flammable
5. The main source of alkanes is from crude oil
6. Insoluble in water
  1. Dissolve in organic solvents
7. Mpt, bpt and density increases with size
CRACKING
1. First, crude oil must be fractionally distilled into 8 fractions
  1. Refinery gas, 2-4 Carbon Atoms.
    1. Bottled Gas
  2. Naphtha, 6-11 Carbon Atoms
    1. Solvents and petrol
  3. Gasoline, 7-10 Carbon Atoms
    1. Fuel for car engines
  4. Kerosene (Paraffin oil) 11-18 Carbon Atoms
    1. Fuel for aircraft and stoves
  5. Diesel oils, 14-20 Carbon Atoms
    1. Fuel for cars and trains
  6. Lubricating oil, 18-25 Carbon Atoms
    1. Lubricants
  7. Fuel oil, 20-27 Carbon Atoms
    1. Fuel for ships and heating
  8. Residue, >35 Carbon Atoms
    1. Road surfaces and roofing
2. It is hard to use long chain alkenes for fuels, as they are too gloopy
  1. Therefore they must be broken down into smaller Alkanes to use for fuels
    1. Alkenes are also a very valuable product of the cracking process
      1. Alkenes can be used to make plastic for rulers (poly)ethene.
        Alkenes do not occur naturally in crude oil
3. Cracking is a thermal decomposition reaction
  1. Large alkane molecules are decomposed by passing them over a heated catalyst at high pressure
    1. It can also be done without a catalyst at very high temperatures
      1. A long chain Alkane breaks down into a shorter chain Alkane AND an Alkene
        C10H22 -> C6H14 + C4H8
        Decane -> Hexane + Butene
        The Carbon and Hydrogen atoms on both sides of the equation must be equal
    2. Aluminium (III) oxide
Fossil Fuels
1. COAL
  1. Mostly plant material
  2. Mainly Carbon
  3. Carboniferous rock
  4. Coal is the worst for the environment as it produces a lot of CO2
    1. It also gives off Soot, Sulphur dioxide and poly-aromatic, carcinogenic hydrocarbons
2. OIL
  1. Mostly plant material
  2. Oil deposits are formed in porous (spongy) rock sediments
    1. They rise until they are stopped by non porous rock e.g: Shale
      1. By drilling through the Shale, the Natural Gas can rise to the top
3. NATURAL GAS
  1. Mostly methane (CH4)
  2. Mostly animal material
4. Remains were buried in sediments
  1. This kept out Oxygen and stopped decaying
    1. Further sedimentary deposits increased pressure
      1. The decomposing gave off heat (like a compost heap).
        This eventually turned them into Coal, Natural Gas and Oil
5. FINITE RESOURCES AND NON-RENEWABLE
6. Crude oil contains hydrocarbons
A HYDROCARBON CONTAINS ONLY CARBON AND HYDROGEN
ISOMERS
1. Isomers have the same MOLECULAR FORMULA but a different STRUCTURAL FORMULA
2. Butane is the first Alkane with an isomer
3. To show isomerism, we must use DISPLAYED FORMULAE
  1. These show EVERY BOND AND ATOM
    1. Each line for a bond in a displayed formula represents a single covalent bond

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Alkanes and Alkenes

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	Created by James Lamming almost 11 years ago