=Formation of Alkenes= Alkenes can be formed by cracking large alkanes (see "Cracking" node). Alkenes can be formed through elimination reactions of alcohols or haloalkanes (see nodes on reactions of alcohols and haloalkanes). =Addition Reactions= A carbon-carbon double bond is a great source of electrons. This double bond may attract atoms that accept electrons, or are highly electronegative. Addition reactions involve the double bond breaking, and forming two new bonds (one new bond for each carbon). ==Addition of Hydrogen== Also known as hydrogenation. Reagents used: high temperatures and a Platinum or Nickel catalyst. Ethene + Hydrogen ---Pt---> Ethane ==Addition of Hydrogen Halides== Halogen Halides can be symbolised as HX, where X is any atom in group 17. Reagents used: none Ethene + Hydrogen chloride --> Chloroethane ==Addition of Water== Also known as a hydration reaction. It is best to think of water consisting of an H and OH group. Reagents used: high temperatures and concentrated sulfuric acid (H2SO4) Ethene + Water --Conc H2SO4/Heat--> Ethanol ==Addition of Halogens== This is a common test to compare with alkanes. Alkenes react with Chlorine or Bromine water rapidly, without a catalyst. This can be observed as a rapid decolourisation of orange bromine water. Ethene + Bromine --> 1,2-dibromoethane ==Addition Polymerisation== Alkenes can create single C-C bonds between molecules. This creates a long chain known as a polymer. For more info, see the Polymer node. =Oxidation of Alkenes= Alkenes react with acidified potassium permanganate. Potassium Permanganate is a strong oxidant, and will initially convert the double bond to two alcohol (OH) groups. Ethene + Acidified Potassium Permanganate --> Ethan-1,2-diol. The purple colour of permanganate will fade as the reaction proceeds.
Credit: Megan Fowler