* Chemical changes involve the formation of new substances with different properties. This usually involves breaking and forming new chemical bonds.

* Physical changes alter the form or appearance of a substance but not its chemical composition.

Let's look at some examples:

Chemical Changes:

* Burning wood: Wood reacts with oxygen, producing ash, smoke, and gases. The original wood is gone, replaced by entirely new substances.

* Baking a cake: The ingredients (flour, sugar, eggs, etc.) undergo chemical reactions when heated, creating a new substance with a different texture, taste, and smell.

* Rusting iron: Iron reacts with oxygen and water to form iron oxide (rust), a new substance with a different color and properties.

Physical Changes:

* Melting ice: Ice changes state from solid to liquid, but it's still water (H2O).

* Boiling water: Water changes state from liquid to gas, but it's still water (H2O).

* Crushing a can: The can changes shape, but its chemical composition remains the same.

To determine if an activity is a chemical change, ask yourself:

* Does it involve a change in the chemical composition of the substance?

* Are new substances formed?

Let me know if you have a specific activity in mind, and I can help you determine if it's a chemical or physical change!