A process that changes one or more substances into new substances is called a chemical reaction.

Here's why:

* Chemical reactions involve the breaking and forming of chemical bonds. This means the arrangement of atoms within the molecules changes, resulting in the formation of entirely new substances with different properties.

* Physical changes only alter the appearance or state of matter, but not the chemical composition. For example, melting ice is a physical change because it's still water (H₂O), just in a different form.

Here are some examples of chemical reactions:

* Burning wood: Wood reacts with oxygen in the air, producing ash, smoke, and carbon dioxide.

* Baking a cake: Flour, sugar, eggs, and other ingredients react to form a cake with a different texture, flavor, and appearance.

* Rusting iron: Iron reacts with oxygen and water to form iron oxide (rust).

Let me know if you'd like more examples or have any other questions!