Chlorination of Alkanes

• What is free radical substitution?

  A reaction where hydrogen is replaced by halogen
• What initiates free radical substitution reactions?

  Ultraviolet (UV) light
• What is the role of light energy in free radical substitution?

  It provides activation energy to break bonds
• What are free radicals?

  Highly reactive species with unpaired electrons
• How are free radicals represented?

  With a dot next to the atom
• Give an example of a chlorine free radical.

  Cl•
• What are the three key stages of the chloromethane synthesis reaction?

  • Initiation
  • Propagation
  • Termination
• What occurs during the initiation stage of chloromethane synthesis?

  Cl₂ absorbs UV light and undergoes fission
• What happens during the first propagation step?

  Cl• reacts with CH₄ to form •CH₃ and HCl
• What is the reaction for the first propagation step?

  Cl• + CH₄ → •CH₃ + HCl
• What occurs during the second propagation step?

  •CH₃ reacts with Cl₂ to form CH₃Cl and Cl•
• What happens during the termination stage?

  Two free radicals combine to form a stable molecule
• Give an example of a termination reaction.

  Cl• + Cl• → Cl₂
• What can occur if chlorine is in excess during free radical substitution?

  • Further substitution can occur
  • All hydrogen atoms can be replaced
  • Final compound can be tetrachloromethane (CCl₄)
• What did scientific research in the 1970s reveal about CFCs?

  They significantly damaged the ozone layer
• What was established in 1987 to phase out CFCs?

  The Montreal Protocol
• What happened to CFC emissions since the early 2000s?

  They have gradually reduced
• What have CFCs been replaced with?

  HCFCs and HFCs
• What is a key feature of HFCs?

  They contain no chlorine and do not deplete ozone
• What is the ozone layer?

  A region in the Earth’s stratosphere
• What is the function of the ozone layer?

  It absorbs harmful UV radiation from the sun
• How is ozone formed in the stratosphere?

  UV light splits O₂ into radicals, forming O₃
• What is the reaction for ozone formation?

  O₂ + O• → O₃
• What is released when CFCs break down?

  Cl• radicals
• What does the Cl• radical do to ozone?

  It reacts with ozone to form ClO• and O₂
• What is the overall reaction for ozone depletion by CFCs?

  2O₃ → 3O₂
• How does the breakdown of ozone by CFCs occur?

  1. CFCs break down under UV light, releasing Cl•.
  2. Cl• reacts with O₃ to form ClO• and O₂.
  3. ClO• reacts with O₃, regenerating Cl• and producing O₂.
  4. This process allows Cl• to continuously deplete ozone.