^ hmm that's not quite right. I'm neglecting work, which is an important factor. Plus, we should know how much "potential heat" is stored in chemical bonds, yet it seems it's impossible to know how much enthalpy a system has.

It's further complicated by things like your comment above...
"It's one of about 30-ish forms energy can take..."

There's lots of forms of energy, but ultimately they fall into one of two categories... kinetic and potential. And even then, whether you observe kinetic or potential energy is frame of reference dependent... it's relative. Energy is complicated as fuck.

I'm going to bed.