Short answer
A physical change alters form or state while the substances remain chemically the same; melting ice is an example. A chemical change forms new substances; iron rusting is an example. Energy can be involved in either kind, so heat alone does not settle the classification. 1 2
The deciding question is whether new substances form, not whether the visible change is dramatic.
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At a glance
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| Question | Physical change | Chemical change |
|---|---|---|
| Chemical identity | Preserved | Changed |
| Example | Ice melting | Iron rusting |
| Must be reversible? | No | No |
The table summarizes the cited definitions and the article’s stated scope. 1 2
What each thing is
Physical change. A change in form, state or properties that does not change the chemical identity of the substances present. 1
Chemical change. A process that creates one or more substances with chemical identities different from the starting substances. 2
Key differences
OpenStax defines physical change by preserved chemical composition and chemical change by formation of different matter. Breaking a glass is dramatic but physical; an invisible reaction in solution can be chemical. 1 2
How to tell them apart
Identify the substances before and after. A state change from water to steam preserves H₂O. A reaction that produces iron oxide changes composition. Bubbles, color or temperature shifts are clues but not conclusive proof by themselves. 1 2
Where they overlap
A real event can contain both types at once. Heating food can melt fats while also causing chemical reactions; classifying the whole process may require separating its parts. 1 2
Edge cases
Dissolving is often physical in introductory examples, but it can accompany chemical reactions or ionization. “Reversible” is not the definition: some physical changes are hard to undo and some chemical reactions can reverse. 1 2
Why the distinction exists
The distinction connects observable events to what happens to the substance itself, which matters for predicting composition and reactions. 1 2
Common misconceptions
A physical change is not necessarily small or easy to reverse. A chemical change is not defined by a color change alone. 1 2
Examples
Cutting paper changes its shape without making a new substance. Burning paper creates gases and ash with different chemical identities. 1 2
Sources
Sources checked October 3, 2026.
- OpenStax — Physical and Chemical Properties. Physical and chemical change.
- OpenStax — Phases and Classification of Matter. Elements and compounds.