In a physical change no new substance is made. Melting, freezing, boiling, dissolving and changing shape are physical changes, and they are usually easy to reverse. The particles stay the same; they are just arranged differently.
In a chemical change, also called a chemical reaction, atoms rearrange to make new substances with different properties. Burning, rusting, cooking an egg and neutralising an acid are chemical changes. They are usually hard to reverse. The starting substances are reactants and the new ones are products. Comparing properties such as colour, density, melting point and smell before and after a change tells you whether a new substance has formed.
Worked example
Ice melts into water. Is this a physical or chemical change?
- Water and ice are the same substance, H₂O.
- Only the arrangement of particles changes.
Answer:It is a physical change.
Key words
- physical change
- no new substance is made
- chemical change
- a new substance is made
- reactant
- a substance at the start of a reaction
- product
- a new substance made in a reaction
New questions every time.
NGSS-referenced: MS-PS1-2