Reaction of alkenes

• Addition reactions

  • alkenes react via addition reactions
  • open up the double bond
  • allows the two carbon atoms to bond with additional atoms
• Addition reaction of alkenes

  • alkenes react via addition reactions
  • opens up carbon-carbon double bond
  • allows the two carbon atoms to bond with additional atoms

  
• Formula of ethene

  • C2H4
• Hydrogenation of alkenes

  • Hydrogen can react with double-bonded carbons to open up the double bond
  • This forms the equivalent, saturated alkane
• Hydrogenation of first four alkenes

  • ethene + hydrogen --> ethane
  • propene + hydrogen --> propane
  • butene + hydrogen --> butane
  • pentene + hydrogen --> pentane
• Hydrogenation of propene

  • propene + hydrogen --> propane

  
• What does the hydrogenation of alkenes take place in?

  • reaction between hydrogen + alkene
  • the presence of a catalyst
• Where is most likely the catalyst coming from in the periodic table?

  • middle block
  • transition metals
• Describe the hydrogenation of ethene

  • Hydrogenating the unsaturated hydrocarbon ethene
  • makes the saturated hydrocarbon ethane
• Hydration of alkenes

  • alkene + water (steam) --> alcohol
• Hydration of ethene

  ethene + water (steam) --> ethanol
• Conditions of hydration of alkenes

  • in a presence of a catalyst
  • steam
  • high temperatures of 300 degrees
• What happens to unreacted alkenes?

  • goes back into the reactor
• Hydration of propene

  propene + water --> propanol

  
• Addition of halogen of alkenes : Halogenalkane


  • chlorine, bromine, iodine can be added to an alkene.
  • reactions are usually spontaneous
• Addition of chlorine to ethene

  • ethene + chlorine --> dichloroethane
• Molecules formed from addition of halogens to alkenes

  • saturated
  • double carbon-carbon bonds each becoming bonded to a halogen atom

  
• Addition polymerisation

  • Alkenes undergo addition polymerisation reactions to form polymers
• Polymers 


  • Molecules made from large numbers of monomers joined together
• Describe addition polymerisation

  • double carbon-carbon bonds allow alkene molecules to join together and form a single product, polymer
• Conditions for addition polymerisation

  • high pressure
  • catalyst
• Addition polymerisation of ethene

  • ethene = monomer
  • poly(ethene) = polymer
• What is 'n'?

  • a very large number
• Why does the repeating unit of a polymer have the same atoms as the monomer?

  • The polymer is the only molecule made in the reaction
• Addition polymerisation of propene

  • square brackets
  • extended lines

  
• What must you do in addition polymerisation?

  • remove the double carbon-carbon bond
  • change to a single carbon-carbon bond
• 3 types of reaction with alkenes

  • hydration (+ water)
  • hydrogenation of alkenes ( + hydrogen)
  • halogen + alkene = halogenalkene