Alkenes

• What type of bond do alkenes have?

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

  They have fewer hydrogens than alkanes
• What happens to the C=C double bond in alkenes during reactions?

  It can open to form single bonds
• What are the first four alkenes?

  Ethene, propene, butene, pentene
• How many hydrogen atoms do straight-chain alkenes have?

  Twice as many as carbon atoms plus 2
• What is the general formula for alkenes?

  C$n$H$2n$
• What is the chemical formula for ethene?

  C$2H$4
• What is produced during the incomplete combustion of alkenes?

  Carbon and carbon monoxide
• How does incomplete combustion of alkenes differ from complete combustion?

  Incomplete combustion produces carbon and CO
• What is the equation for the incomplete combustion of butene?

  C$4H$8 + 5O$2$ → 2C + 2CO + 2CO$2$ + 4H$2O$
• What are the key properties of alkenes?

  • Hydrocarbons with a C=C double bond
  • Unsaturated due to fewer hydrogens
  • More reactive than alkanes
  • React via addition reactions
• What is hydrogenation in relation to alkenes?

  Addition of hydrogen to double-bonded carbons
• What is produced when ethene reacts with steam?

  Ethanol
• How is ethanol produced industrially from ethene?

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

  It is recycled back into the reactor
• Which halogens can react with alkenes?

  Bromine, chlorine, and iodine
• What is the result of bromine reacting with ethene?

  Dibromoethane is formed
• How can bromine water be used to test for alkenes?

  It decolourises when added to alkenes
• What colour change occurs when butene reacts with bromine water?

  From orange to colourless
• What is the word equation for propene reacting with hydrogen?

  Propene + Hydrogen → Alkane
• What is the displayed formula for propene?


  H H H
• What is the displayed formula for the product of propene and hydrogen reaction?

  R-C-C-H