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