Here's a possible solution to address matter conversion.
Rather than have the game always choose the top gas to be the one that wins, what if instead the game selects the winning gas at random (maybe weighting the choice based on mass of the interacting gasses). Then players cannot 100% guarantee which gas will win, which will break any machine design to "exploit" this mechanic. Mass will be preserved. If the RNG weights the choice based on mass, then the expected m