8.73a

[Alyssa Parry Disc 1H]

In this question why are there no h-c bonds broken or formed? Are they just unimportant?

[Tanaisha Italia 1B]

They are important, but if you broke those bonds, you'd just have to form them again. Each carbon is still has to be attached to a hydrogen, so it's easier to just keep those c-h bonds intact.

[Tanaisha Italia 1B]

Actually, you could put the h-c bonds in the broken bonds category and calculate the enthalpies, but you would have to put them in the bonds formed category as well, since the structure denoted on the right side of the equation is benzene (ring structure with carbon-carbon bonds and each carbon bonded to a hydrogen). If you did that, the enthalpies of c-h bonds formed (negative no.) and c-h bonds broken (positive no.) would just cancel each other out.