1) The chain reaction accounts for the observation that the light-promoted reaction
is highly efficient.
- Chain-terminating steps: used up one or both radical intermediates.
H C +
H
H
Cl C Cl
H
H
H^
H C +
H
H
CH
H
H
C
H
H
H
C
H
H
H^
Cl + Cl Cl Cl
1) Chloromethan and ethane, formed in the terminating steps, can dissipate their
excess energy through vibrations of their CāH bonds.
2) The simple diatomic chlorine that is formed must dissipate its excess energy
rapidly by colliding with some other molecule or the walls of the container.
Otherwise it simply flies apart again.
- Mechanism for the formation of CH 2 Cl 2 :
Step 2a
+ H C H
Cl
Cl Cl Cl
H
+ C
H
H
H
Step 3a
+ C +
H
Cl Cl Cl Cl Cl Cl
H
C
H
H
10.5 CHLORINATION OF METHANE: ENERGY CHANGES
- The heat of reaction for each individual step of the chlorination:
