Chemical Properties of Alkene



  • Combustion of alkene involves the reaction of an alkene with oxygen gas in the air.
  • Complete combustion of an alkene is when the oxygen gas is in excess.
  • The products of complete combustion of alkene are carbon dioxide gas and water.
  • Example of the complete combustion of ethene;
Chemical equation for complete combustion of ethene
\(C_2H_4(g) + 3O_2(g) \rightarrow 2CO_2(g)+ 2H_2O(l)\)


  • In the case of insufficiency of oxygen gas, the incomplete combustion of alkene occurs.
  • The products such as carbon monoxide and carbon might be formed from incomplete combustion of the alkene.
  • Example of the incomplete combustion of ethene;
Chemical equation for incomplete combustion of ethene

\(C_2H_4(g) + O_2(g) \rightarrow 2C(s)+ 2H_2O(l)\)


\(C_2H_4(g) + 2O_2(g) \rightarrow 2CO(g)+ 2H_2O(l)\)


Addition reaction

  • Definition: a reaction where other atoms are added to a molecule.
  • The double bond in the alkene makes the compound reactive.
  • The addition reaction occurs at the double bond of the compound.


Reaction of alkene with


  • Reaction with halogen (chlorine, bromine) at room condition.
  • This reaction is also called the halogenation reaction.
  • Product: Haloalkane
  • \(C_2H_4(g) + Cl_2(g) \rightarrow C_2H_4Cl_2(g)\)


  • Catalyst: platinum, Pt or nickel, Ni
  • Temperature: 180°C
  • This reaction is also called a hydrogenation reaction.
  • Product: Alkane
  • \(\, \\C_2H_4(g) + H_2(g) \xrightarrow []{Pt\,or\, Ni}C_2H_6(g)\)


  • Catalyst: phosphoric acid
  • Temperature: 300°C
  • Pressure: 60 atm
  • This reaction is also called the hydration reaction.
  • Product: Alcohol
  • \(\,\\C_2H_4(g) + H_2O(l) \xrightarrow []{H_3PO_4}C_2H_5OH(l)\)

Acidified potassium manganate(VII) solution

  • Acidified potassium manganate(VII) solution is a very good oxidising agent.
  • This reaction is also called the oxidation reaction.
  • Product: Diol (Alcohol with two hydroxyl groups)
  • \(C_2H_4(g) + H_2O(l) \xrightarrow []{[O]} CH_2OHCH_2OH(l)\)



  • The pair of electrons making up one of the double bonds is shared with the carbon atom of another alkene molecule in the polymerisation reaction.
  • Example: polymerisation of ethene;
    • Polymer: polyethene
    • Monomer: ethene
    • Pressure: 2000 atm
    • Temperature: 100°C to 300°C