Mechanism for Phosgene Formation

[chemkid01]

The overall reaction for the formation of phosgene from Cl2 and CO is:

Cl2 + CO --> Cl2CO

The mechanism is:

Cl2 + M <--> 2Cl' + M
Cl' + CO <--> ClCO'
ClCO' + Cl2 --> Cl2CO + Cl'

For this mechanism, the sum of the elementary reactions is:

2Cl2 + CO --> Cl2CO + 2Cl'

However, doesn't the sum of the elementary reactions need to add up to the overall reaction?

 

[Quantum Defect]

The overall reaction for the formation of phosgene from Cl2 and CO is:

Cl2 + CO --> Cl2CO

The mechanism is:

Cl2 + M <--> 2Cl' + M
Cl' + CO <--> ClCO'
ClCO' + Cl2 --> Cl2CO + Cl'

For this mechanism, the sum of the elementary reactions is:

2Cl2 + CO --> Cl2CO + 2Cl'

However, doesn't the sum of the elementary reactions need to add up to the overall reaction?

Multiply reaction 2 and 3 by 2 and add these together with one and you will be get the net reaction. Remember that in real systems, you will have lots of reactions. Adding all of the possible reactions together doesn't necessarily give you the net reaction. E.g in the system above, you will also have recombination -- the reverse of reaction one. You could also add reaction -1 to what you have to get the net reaction. This does not mean that this is what the atoms are doing.

 

[chemkid01]

Got it, thank you!