Question about Calculating Bond Energies

[Lori]

Homework Statement

Part of a chemical equation, but i had to calculate the bond energies in C2H6,

Homework Equations

im given that C-H bonds are 414 kj/mol[/B]

The Attempt at a Solution

and that i know there are 6 of these based on the lewis structure, but how come i don't have to include C-C bond energy? I wasnt given the bond energy for this. C2H6 was part of a chemical equation in which i had to calculate the bond energy for to find change in H[/B]

 

[Lori]

Is it because if the elements are the same, then there is no bond energy? Cause i know that elements have 0 heat of formation

 

[Borek]

Definitely not zero. Can you show whole question, perhaps C-C bond can be somehow ignored?

 

[Lori]

Definitely not zero. Can you show whole question, perhaps C-C bond can be somehow ignored?

Hopefully you can see the question in the pic. It's question 16. Calculate change in H.

 

[Borek]

Too small for details, but I still think C-C bond energy cancels out.