An age old problem that I’ve become a little weary of addressing, so let’s clear this up really quickly and really simply.

No biologists, breaking bonds does NOT ‘release energy’, and here’s why.

No biologists, breaking bonds does NOT 'release energy'Bond breaking is an endothermic process (+ve), and bond making is an exothermic process (-ve). All chemical reactions involve both processes, and the enthalpy change for the reaction is always a SUM of those processes. Biologists choose to ignore the individual breaking and making of bonds during a chemical reaction, and they choose to only report the SUM of these processes, i.e., the enthalpy change, which is fine. However, then they go on to incorrectly label the overall enthalpy change as simply ‘bond breaking’ or ‘bond making’ – that’s plain wrong since they are ignoring the fact that BOTH processes contribute to the overall enthalpy change.

I have no problem with the biologists ignoring the individual processes if that suits them and their own needs, but the problem is with their incorrect labeling of a chemical reaction as only one or the other; it isn’t, it’s both.

As an aside, I am in the habit of teaching enthalpy changes that involve bond breaking and bond making in a manner that is slightly different to most chemistry teachers in the USA. By teaching that a positive number is associated with bond breaking, and that a negative number is associated with bond making, and that ∆H is the SUM of the two, I try to emphasize a knowledge of the endothermic/exothermic nature of bond breaking/making. In my experience, most chemistry teachers don’t do that, rather they tend to say that ∆H = bonds broken MINUS bonds made. Of course this ultimately yields the same answer, but I find that my method tends to help cement an idea that would help this biology based misconception.