* Chemical change: Involves the formation of new substances with different chemical compositions. This often involves breaking and forming new chemical bonds.

* Physical change: Alters the form or appearance of a substance but doesn't change its chemical composition.

When you melt iron, you're simply changing its state from solid to liquid. The iron atoms themselves remain the same. The chemical composition (iron, Fe) doesn't change. It's just the arrangement of the atoms that changes.

Here's a simple way to remember:

* Melting, freezing, boiling, and condensing are all physical changes.

* Burning, rusting, and cooking are examples of chemical changes.