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Matter and changes
Matter has mass and occupies space. Solids, liquids and gases differ in how particles are arranged and move. A physical change alters form or state; a chemical change produces different substances.
A visible change alone is not enough to classify every process. Melting ice changes state, while rusting iron involves a chemical reaction. Mass measurements require an appropriate closed system when gases enter or leave.
Worked example
Water freezing remains water. Iron reacting with oxygen forms iron oxides.
Try it yourself
List three changes at home and explain whether each is physical or chemical.
Check your understanding
Which is a physical change?
Melting changes the state of water without changing its chemical identity.
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