Preparing Alkene

Alkene can be prepared by

dehydration of alcohol
craking of alkane

Dehydration of Alcohol

When alcohol is heated, it will decompose to form alkene and water. For example, heating ethanol will produce ethene, heating propanol will produce propene, and so on. This process is called dehydration of alcohol.

Dehydration of Ethanol

C₂H₅OH → C₂H₄ + H₂O

Dehydration of Propanol

C₃H₇OH → C₃H₆ + H₂O

Dehydration of Alcohols Using Aluminium Oxide as Catalyst

Catalyst:
Aluminium oxide/ Porcelain chips

Dehydration of alcohols using an acid catalyst

Catalyst:
Sulphuric acid or Phosphoric acid

Temperature: 170°C

Cracking of Alkane

Cracking is the name given to breaking up large hydrocarbon molecules into smaller and more useful bits.
This is achieved by using high pressures and temperatures without a catalyst, or lower temperatures and pressures in the presence of a catalyst.

Example: Cracking of butane

Cracking of butane produces a mixture of methane, ethane, ethene and propene.