* New substances are formed: When magnesium burns, it reacts with oxygen in the air to form magnesium oxide (MgO). This is a completely different substance with different properties than the original magnesium.

* Chemical bonds are broken and formed: The chemical bonds holding magnesium atoms together and the bonds holding oxygen molecules together are broken. New bonds are formed between magnesium and oxygen atoms to create magnesium oxide.

* Energy is released: Burning is an exothermic reaction, meaning it releases heat and light. This energy change is a strong indicator of a chemical reaction.

In contrast, a physical change would only alter the form or appearance of the substance, not its chemical composition. For example, melting ice is a physical change because it's still water (H₂O), just in a different state.