Photochlorination of Methane

• The three stages of the photochlorination of methane are initiation, propagation and termination.
• The initiation stage involves homolytic fission of the Cl-Cl bond to produce two chlorine free radicals.
• In the initiation stage, the Cl-Cl bond is weaker than the C-H bond in methane which means that it breaks first.
• The conditions for the initiation stage are UV light and room temperature.
• Why does the Cl-Cl bond break first in the initiation stage?

  It is weaker than the C-H bond in methane and so it breaks first.
• Why is UV light used in the initiation stage?


  UV light is used because the mechanism requires the formation of free radicals.
• The propagation stage is where a free radical reacts and another is produced (chain reaction).
• The propagation stage has four possible stages that each contains two steps, (one hydrogen atom is substituted by a chlorine atom in each stage).
• The termination stage is where two free radicals react together to produce a molecule and are removed.
• Where have the two free radicals, used in the termination stage, been produced?

  In the propagation steps.