What is the bond energy?

[MedPR]

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What is the bond energy of the second pi-bond in nitrogen gas.

N2 (triple bond) BE is 941
N=N BE is 418
N-N BE BE is 160

Answer choices are:

A: 358
B. 390
C. 313
D: 523

Will post the right answer in a little while.

 

[MT Headed]

N-N is just a sigma bond
N=N is a sigma and one pi
N2 is a sigma and two pi's

The difference between having the second pi and not having the second pi is 523.

 

[MedPR]

N-N is just a sigma bond
N=N is a sigma and one pi
N2 is a sigma and two pi's

The difference between having the second pi and not having the second pi is 523.

You're right, but why doesn't the sigma bond affect the pi bonds at all?

Isn't the BE for N2 the same as the BDE for all 3 bonds to be broken? So shouldn't the BE for the second pi bond be 941-(418+160)?

TBR basically explains that the sigma BDE is insignificant.

 

[SaintJude]

I just figured
Triple bond = 1 sigma + 2 pi bonds = 941
Double bond = 1 sigma + 1 pi bond = 418
So 2ndpi bond must equal difference =523

FOLLOW-UP Q: Is this 2nd pi bond occupying the "anti-pi bonding orbital?"

 

[MT Headed]

418+160 would be the energy of a (sigma+pi)=418, and another sigma=160. It doesn't have much relevance to anything.

The question only asked for the energy of the second pi. So I looked for the energy of a situation that does not contain a second pi, and another scenario that is just like the first scenario except it also has the second pi. Any difference between these two scenarios must be the fault of the second pi bond.