Skill 19.2 Distinguish between physical and chemical changes

Skill 19.2 Distinguish between physical and chemical changes. 

Compare these two nails.They are still iron nails, made of iron atoms. The difference is that one is bent while the other is straight. This is a physical change. 

A chemical change is a chemical reaction. It converts one substance into another because atoms are rearranged to form a different compound. Paper undergoes a chemical change when you burn it. You no longer have paper. A chemical change to a pure substance alters its properties. 

An iron nail rusts to form a rusty nail. The rusty nail, however, is not made up of the same iron atoms. It is now composed of iron (III) oxide molecules that form when the iron atoms combine with oxygen molecules during oxidation (rusting). 

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