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Shaping materials
Words to learn: chemical change • reaction • irreversible • new substance
Burning, rusting and cooking can make new substances. What does that mean for the material afterwards?
A new substance can form
When wood burns it forms ash and gases. When iron rusts it reacts with oxygen. The products have different properties from the starting materials.
Why we cannot simply reverse it
Cooling ash does not turn it back into wood, and reshaping rust does not restore the iron. The atoms have been rearranged into different substances.
But “irreversible” does not mean useless
A material that cannot be changed back may still be useful, reusable in another way, or recyclable by an industrial process. The important question is what we can sensibly do with it next.
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Where does this mystery belong?
CHANGING MATERIALS — TEXTBOOK PAGES TO BE LINKED. Textbook spread and protected page link to be added.
Who uses this knowledge?
