Alkenes

• Alkenes


  • unsaturated hydrocarbons
  • contain at least 1 carbon-carbon double bond
  • general formula CnH2n (n is no. of carbon atoms)
• Physical Properties(Alkene)


  • simple discrete molecules with weak intermolecular forces of attraction
  • Low mp and bp, small amount of energy needed to overcome weak intermolecular foa between alkene molecules
  • mp and bp increase down the homologous series, intermolecular foa between alkene molecules increase as molecular size increases, more energy required to overcome intermolecular foa
  • flow less easily as relative molecular mass increases, intermolecular foa becomes stronger. Viscosity increases down the homologous series
  • insoluble in water
  • soluble in organic solvents
• Chemical Properties (Alkenes)


  • Alkenes undergo complete combustion in the presence of oxygen to form carbon dioxide and water
  • Alkenes burn with smokier and sootier flame than alkanes as they contain higher percentage by mass of carbon compared to corresponding alkanes
  • Undergo addition reactions as they contain carbon-carbon double bonds which are reactive
• Addition Reaction


  • Atoms of reactant can be added across a carbon-carbon double bond in alkene to form a single saturated product
  • Bromination (Addition of liquid bromine)
  • Hydration (Addition of steam)
  • Hydrogenation (Addition of hydrogen)
  • Addition polymerisation
• Bromination


  • Alkenes react with liquid bromine at room temperature
  • When Alkenes are bubble through liquid bromine, red-brown solution is decolourised or turns colourless
  • Forms dibromo alkane
• Hydration


  • Alkenes react with steam to produce alcohols
  • Conditions : 300 degree Celsius, 60 ATM, phosphoric(V) acid catalyst (H3PO4)
• Hydrogenation


  • Alkenes react with hydrogen gas to form alkanes
  • Conditions : 150 degree celcius and nickel catalyst
  • Each carbon-carbon double bond in an alkene reacts with one mole of hydrogen
  • Number of mole of hydrogen reacted indicates the number of carbon-carbon double bonds present in an alkene
• Addition Polymerisation


  • alkene molecules combine to form a long-chain molecule called a polymer
  • Conditions : High temperature, high pressure, catalyst