Properties of Alkenes :
Unaturated hydrocarbons
General formula : CnH2n
Alkenes are made by cracking alkanes. Long alkene molecules are passed over a heated catalyst consisting of Silicon (IV) Oxide and Aluminium Oxide.
C10H22 -> C8H18 + C2H4
Decane -> Octane + Ethene
Hydrogen can also be made by cracking :
C10H22 -> C7H14 + C3H6 + H2
Decane -> Alkene + Alkene + Hydrogen
Cracking is used to make :
- Alkenes
- Hydrogen
- Petrol from higher fractions
Addition Reaction :
Hydrogenation
Condition - 180 degree celsius, Nickel catalyst
Alkene + Hydrogen -> Alkane
Hydration
Condition - 300 degree celsius, Phosphoric Acid, 60 atmospheric pressure
Alkene + Water -> Alcohol
Test for an alkene
When a few drops of Bromine water are added to a tube of ethene gas, the colour changes from brown to colourless.
Ethene + Bromine -> Dibromoethane