Ice, Water, Steam: The Shape Shifters
Explore reversible physical changes in states of matter
Setting up the bench…
What this lesson covers
Why it matters
Melt an ice cube and you can freeze it right back. Burn a matchstick and there is no un-burning it. Some changes have an undo button; some don't.
Predict first
Which kind of change can usually be undone?
Physical changes (melting, boiling, dissolving) are usually reversible — same substance, new form. Chemical changes (burning, rusting, cooking) make new substances and are hard to reverse.
- A physical change — no new substance forms — correct
- A chemical change
- Any change, given enough heat
What you do
Every physical change has an undo button. Match each change with the reverse change that brings the substance back.
Check yourself
Which change is reversible?
Melted ice can be re-frozen; burning and cooking form new substances.
A change is usually irreversible when…
Making a new substance is what makes a change hard to undo.
- Melting of ice — correct
- Burning of wood
- Cooking an egg
- a new substance is formed — correct
- only the shape changes
- it happens quickly