Candle cracker - outwards force Heat a small amount of water in a cylinder. The vaporized steam pushes the piston out. The air pressure shatters the bottle. Note that the reaction is exothermic. Sufficient heat is released to ignite white phosphorus.
Water is given off.
This shows the reversibility of the reaction. But it is really a compound body and we can decompose and recompose it at pleasure Heat blue hydrated copper sulfate. Notice the water and the white, anhydrous copper sulfate that is produced. Add water back to the anhydrous copper sulfate. Note that the oxygen required for combustion comes from the air.