Answer:
Step-by-step explanation:
A photochemical reaction is a chemical reaction that occurs due to the absorption of light energy. These reactions typically require high-energy radiation, such as ultraviolet or visible light, to initiate the reaction.
The three stages involved in the photochemical reaction between methane and chlorine to form chloromethane are:
i) Initiation: Chlorine molecules absorb high-energy UV radiation, which causes the chlorine bond to break homolytically, producing two chlorine radicals. This process requires energy and is endothermic.
Cl2 + energy (UV) → 2Cl•
ii) Propagation: The chlorine radical attacks a methane molecule, breaking the C-H bond and producing a methyl radical and HCl. The methyl radical then reacts with another chlorine molecule, producing another chlorine radical and chloromethane. The chlorine radical then continues to react with more methane molecules, propagating the reaction.
Cl• + CH4 → •CH3 + HCl
•CH3 + Cl2 → CH3Cl + Cl•
iii) Termination: In the termination stage, radicals combine to form products, which stops the propagation of the reaction. For example, two methyl radicals can combine to form ethane, or a chlorine radical and a methyl radical can combine to form methyl chloride.
•CH3 + •CH3 → C2H6
•CH3 + Cl• → CH3Cl
The overall reaction for the formation of chloromethane from methane and chlorine in the presence of UV light is:
CH4 + Cl2 + UV light → CH3Cl + HCl