Let's test three everyday changes against our signs. Watch how each one makes something new.
| Change | Signs of new substance | Can you undo it? |
|---|---|---|
| Burning toast | colour change (black), smoke (gas), heat | No — you can't un-burn toast |
| Rusting iron | new material (orange rust), colour change | No — rust is a new substance (iron oxide) |
| Cooking an egg | colour change (clear→white), new texture | No — you can't un-cook an egg |