* Chemical changes involve the formation of new substances with different chemical compositions. For example, burning wood creates ash, carbon dioxide, and water - completely different substances from the original wood.

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

When water freezes into ice:

* The chemical formula (H₂O) remains the same. Ice is still made of hydrogen and oxygen atoms bonded together in the same way as liquid water.

* The physical arrangement of the molecules changes. Water molecules in ice are more organized and spaced farther apart than in liquid water, leading to the solid form.

Think of it this way: You can easily melt ice back into water, demonstrating that no new substance was created. This reversibility is another key characteristic of physical changes.