Yeah! That’s what I’m talking about!

That checks out

The reaction from limestone with water is exothermic. As an example. Limestone is plentiful, water is plentiful. I guess the point of a chemical reaction is that it eventually we just run out of reactants. And that is not sustainable.

I wonder if there was some kind of recycling loophole you could design for a very low loss energy production cycle. Seems like it should be possible at least somehow.

Yes, functionally, from an engineering perspective there is a finite number of ways that molecules can get together or energies can be applied to said molecules.

Finding new materials or new compounds or manufacturing new compounds is often how we drive technological innovation.