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Chapter 23- Alkenes

  • Alkenes are unsaturated hydrocarbons with double bonds between two carbon atoms.

  • The general formula is CnH2n

  • Isomers of alkenes can be formed by branching them or changing the position of the double bond.

  • Catalytic cracking is used to manufacture alkenes from alkanes. It can also be used to manufacture hydrogen.

  • An alkane can be broken in three ways using cracking: Making one alkane and one alkene, and one hydrogen, making two alkenes and hydrogen, making an alkane.

  • Alkenes can also be combusted.

ADDITION REACTIONS OF ALKENES

  • Alkenes undergo addition reactions, i.e. reactions where only one product is formed. Double bonds are broken into single bonds.

  • HYDROGENATION: In presence of the catalyst nickel and 200 degrees celsius temperature, alkenes react with hydrogen to form alkanes.

  • Used in manufacture of margarine from vegetable oil.

  • BROMINATION: when bromine is added to an alkene, it immediately decolourises as the double bonds are broken and bromine atoms join the alkene.

  • Used in the test for saturation as bromine water decolourises in unsaturated substances only.

  • HYDRATION: In the presence of phosphoric (V) acid, 300 degrees celsius temperature and 60 atm pressure, alkenes react with steam to form alcohols.

Chapter 23- Alkenes

  • Alkenes are unsaturated hydrocarbons with double bonds between two carbon atoms.

  • The general formula is CnH2n

  • Isomers of alkenes can be formed by branching them or changing the position of the double bond.

  • Catalytic cracking is used to manufacture alkenes from alkanes. It can also be used to manufacture hydrogen.

  • An alkane can be broken in three ways using cracking: Making one alkane and one alkene, and one hydrogen, making two alkenes and hydrogen, making an alkane.

  • Alkenes can also be combusted.

ADDITION REACTIONS OF ALKENES

  • Alkenes undergo addition reactions, i.e. reactions where only one product is formed. Double bonds are broken into single bonds.

  • HYDROGENATION: In presence of the catalyst nickel and 200 degrees celsius temperature, alkenes react with hydrogen to form alkanes.

  • Used in manufacture of margarine from vegetable oil.

  • BROMINATION: when bromine is added to an alkene, it immediately decolourises as the double bonds are broken and bromine atoms join the alkene.

  • Used in the test for saturation as bromine water decolourises in unsaturated substances only.

  • HYDRATION: In the presence of phosphoric (V) acid, 300 degrees celsius temperature and 60 atm pressure, alkenes react with steam to form alcohols.