My students don't get credit, not even partial
credit, for PbBA.
Would somebody care to take a stab at giving
a _reason_ (you know, a physics reason) why
we must represent chemical-bond energy levels
as negative?
In addition to innumerable manifestly incorrect
and implausible formulations, there are two fairly
plausible formulations to consider:
1) A weak bond has a smallish negative energy,
while a strong bond has a more-negative energy.
2) A weak bond has a higher positive energy,
while a strong bond has a less-positive energy.
I think we all agree that formulation (1) is allowed
by classical physics. If there is a reason why
formulation (2) is not AT LEAST as allowable, I
haven't seen it.
(In fact what little I know about general
relativity seems to favor formulation (2),
although this is irrelevant to chemistry by
many orders of magnitude.)
=================
It would clearly be a fallacy to speak of releasing
energy by breaking bonds. But the fallacy attaches
to the breaking, not to the bonds. Combustion involves
breaking weak bonds and replacing them with stronger
bonds, and it is the _last_ step that liberates energy.