reactions of alkanes

• alkanes are very unreactive

  • they undergo combustion and reactions with halogens
• combustion is an oxidative reaction

  • complete combustion occurs with plentiful supply of air with carbon dioxide + water as products

  -> colour of the bunsen burner flame is blue flame

  • incomplete combustion occurs in a limited supply of oxygen with carbon monoxide, carbon dioxide + water

  -> colour of bunsen burner flame is dirty yellow flame

  -> longer chains hydrocarbon are most likely to undergo incomplete combustion
• • environmental impact of carbon monoxide is that it is toxic
  • environmental impact of soot is asthma, cancer + global dimming
• halogenoalkanes are formed from alkanes by radical substitution
• alkane reacts with halogens in the presence of UV light

  • initiation - breaking halogen bond to form free radicals
  • propagation - chain part of reaction where products are formed but free radical remains
  • termination - free radicals removed, stable products formed
• Chlorination of methane to for Chloromethane

  Initiation: Cl, → 2Cl• (in presence of UV light)

  Propagation:

  • Cl• + CH4 → HCl + •CH3
  • •CH3 + Cl2 → CHCI + Cl•

  Termination:

  • •CH3 + Cl• - CH3CI
  • 2Cl• → Cl2
  • •CH3 + •CH3 → CH3CH3
• because they only want one desired product , it has low atom economy because a mixture of products is produced by the random collisions between radicals