On puzzle 68: Part of me wants to introduce an energy term, but that would just end up as another kind of raw material. So what we're really looking for is Petri-reachability.

Edit: I think I misread the question, I didn't realize that the only reaction to be considered is the first \\(H_2O\\) diagram. I'm still not sure I know what John meant, I'll have to try again later. Thanks to Michael Hong for his proposed solution, which made me doubt everything!