Alkenes and their reactions

• What type of bond do alkenes have?

  Double carbon-carbon bond
• Why are alkenes considered unsaturated?

  They have fewer hydrogen atoms than alkanes
• What does the C=C double bond in alkenes allow?

  It allows bonding with other atoms
• What are the first four alkenes?

  Ethene, propene, butene, pentene
• What is the general formula for alkenes?

  C_nH_2n
• What are the formulas for the first four alkenes?

  • Ethene: C₂H₄
  • Propene: C₃H₆
  • Butene: C₄H₈
  • Pentene: C₅H₁₀
• How do alkenes differ from alkanes?

  Alkenes have a C=C bond, alkanes do not
• What happens during the combustion of alkenes in a large amount of oxygen?

  They combust completely to produce water and carbon dioxide
• What occurs during incomplete combustion of alkenes?

  Carbon and carbon monoxide are produced
• What is the standard equation for incomplete combustion of alkenes?

  alkene + oxygen → carbon + carbon monoxide + carbon dioxide + water
• What does incomplete combustion of alkenes result in?

  A smoky yellow flame and less energy
• What is a functional group?

  A group of atoms that determines reactivity
• How do alkenes typically react?

  Via addition reactions
• What happens to the carbon-carbon double bond during addition reactions?

  It opens up to form a single bond
• What is hydrogenation in relation to alkenes?

  Addition of hydrogen to form alkanes
• What do halogens do when they react with alkenes?

  They bond to the C=C carbons
• What is formed when bromine reacts with ethene?

  Dibromomethane
• How can bromine water be used to test for alkenes?

  It decolourises when added to alkenes
• What happens when bromine water is added to a saturated compound?

  It stays bright orange
• What occurs when alkenes react with steam?

  They form alcohols
• How is ethanol produced from ethene?

  By mixing ethene with steam over a catalyst
• What happens to the reaction mixture after producing ethanol?

  It is condensed and unreacted ethene is recycled
• What is the test for distinguishing between alkanes and alkenes?

  • Bromine water test:
  • Alkane: stays orange
  • Alkene: turns colourless