Metals that fight with water, things that burn, and the oxidizers you do not try at home.
Drop an alkali metal on water and it makes hydrogen fast enough to light itself. Sodium pops, calcium fizzes.
Making it, catching it, and setting it off. Electrolysis, drain cleaner and foil, and the hydrogen candle.
A metal that burns so hot it keeps going in dry ice, in nitrogen, and inside a pumpkin.
Potassium permanganate is a strong oxidizer. Give it glycerin, honey, or syrup and wait for the purple volcano.
What burning actually is: fuel, oxygen, heat, and the products you can weigh afterwards.
Iron burns. It also gains weight while it does, which is the best conservation-of-mass lesson there is.
The five kinds of chemical reaction, how fast they go, and what temperature does to that.