Quote Originally Posted by OngBonga View Post
^ 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.
Yeah. Energy is at the same time very simply and very mysterious, IMO.
On the one hand it's just energy. You know when you have energy and when you don't. You understand it takes energy to "do stuff" which is basically the best definition of energy out there: the ability to do stuff.

On that hand, it's very simple.
On the other hand, it's so sneaky in how it transforms and hides from us that it becomes mysterious again, like... how can the change in potential energy correspond to a change in kinetic energy and why not in thermal energy? Why is it when I throw something up in the air, it slows down, rather than grows cold? How does energy know what form to change into and when and how much?
Mysterious again.

I don't mind the game of putting energy into categories. It's a physics tradition, after all.
I find it more useful to think of the 2 categories as energies that result from conservative fields and energies that result from non-conservative fields.
Like, gravitational potential energy and spring potential energy are conservative fields. They are path independent - meaning that if you start at one position and move through any simple or complicated path to another position, the change in energy is always the same. The path doesn't matter.
Contrast to energy lost due to friction. Friction happens over distance. If you take a longer path to get to the same destination, you probably lost more energy to thermal heating caused by friction. The path matters.