Direct comparison
Physical vs chemical change
A physical change alters a substance’s form or state without creating new substances; a chemical change rearranges atoms to form new substances.
The step most authors miss
Doing CRediT right? Don’t stop at the statement.
A CRediT statement credits you inside one paper. The recognition CRediT was built for happens when those roles are tied to you, persistently. Sign in with your ORCID — free — and claim your CRediT contributions on casrai.org, the home of the standard. They become a verified, portable part of your identity, not a line that disappears into one PDF.
Free: claim your contributions, then export a journal-ready CRediT statement, schema.org structured data, JATS XML, CSV or BibTeX — and preview your public profile. A membership publishes that profile publicly and verifies the journals you serve.
Side-by-side comparison
| Dimension | Physical change | Chemical change |
|---|---|---|
| New substance formed? | No — the substance keeps its chemical identity. | Yes — one or more new substances are produced. |
| What changes | State, shape, size or appearance. | The chemical composition and bonding. |
| Reversibility | Often easily reversed (e.g. freezing then melting). | Usually hard to reverse by simple means. |
| Bonds | Chemical bonds within molecules stay intact. | Bonds are broken and new bonds are formed. |
| Mass | Conserved. | Conserved (atoms are rearranged, not created or destroyed). |
| Energy change | Usually small and tied to state change. | Often a larger energy release or absorption. |
| Signs to watch for | Melting, boiling, dissolving, crushing, magnetising. | Colour change, gas bubbles, precipitate, heat or light, odour. |
| Example | Ice melting, sugar dissolving, paper being torn. | Iron rusting, wood burning, milk souring. |
| Tricky case | Dissolving salt in water — separable by evaporation. | Electrolysis of water — produces hydrogen and oxygen. |
The reliable test: did the chemical identity change?
The single question that separates the two is whether new substances with new chemical properties have appeared. Signs that often accompany a chemical change include a colour change, the release of a gas, the formation of a solid precipitate from solutions, an unexpected temperature change, or the release of light. None of these is foolproof on its own — boiling water bubbles without any chemistry occurring, and mixing coloured liquids changes colour physically — so they are clues rather than proof. The decisive criterion remains the formation of a chemically different substance.
Common questions
FAQ
Is dissolving a physical or chemical change?+
Dissolving most substances, such as salt or sugar in water, is generally a physical change: the substance disperses but keeps its chemical identity and can be recovered, often by evaporating the water. Some dissolving does involve chemistry — for example, certain metals reacting with acid as they dissolve — but everyday dissolving of salt or sugar is treated as a physical change.
Is boiling water a chemical change?+
No. Boiling water is a physical change. The water turns from liquid to gas (steam), but it is still water — the same H₂O molecules, just spread further apart. No new substance is formed, and cooling the steam turns it straight back into liquid water. Only splitting water into hydrogen and oxygen would be a chemical change.
Are all chemical changes irreversible?+
Not strictly, but they are far harder to reverse than physical changes. Many can in principle be undone by another chemical reaction — for example, electrolysis can reverse some combinations — but you cannot simply cool or re-melt your way back as you can with a physical change. In everyday terms, chemical changes are treated as effectively irreversible.
Going deeper
