* New substances are formed: The chemical compounds in fireworks (gunpowder, oxidizers, colorants) react to produce entirely new substances like gases, smoke, and ash.

* Irreversible: You can't easily reverse the explosion and get back the original ingredients.

* Energy release: The chemical reactions release a significant amount of energy, causing the explosion and light show.

In contrast, a physical change would be something like:

* Melting ice (water changes state, but its chemical composition remains the same).

* Cutting paper (you're changing the shape, but not the chemical makeup of the paper).