This lesson is already hands-on; deepen it by making students physically prove the "you can get it back" test at every station.
The "undo it" challenge
At each station, students don't just observe the change — they physically attempt to reverse it and check the substance returns. Melt the chocolate, then cool it and confirm it's solid chocolate again; dissolve the salt, then leave a drop to evaporate on a warm tile and find the salt crystals reappear. The act of undoing it is the evidence that the substance never changed.
Body model of states
Students model particles with their bodies: huddled and still (solid), holding hands but moving (liquid), spread out and zooming (gas). On your cue "heat!" they spread out; on "cool!" they pull back together — feeling that melting and freezing just rearrange the same particles without changing what they are.