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GCSE Physics · key term
A change in which one or more new substances with different properties are formed.
Used by AQA and OCR
Specification 4.3.1.2 · Paper 1
A change that forms one or more new substances with different properties.
Revise: Changes of stateThis distinguishes a change of state from a chemical change. In a chemical change, new substance or substances are formed. Reversing a state change restores the same material because its particles never changed chemical identity; only their physical arrangement and movement changed.
Specification P1.2b · Paper 1 (Foundation), Paper 3 (Higher)
Revise: Physical vs chemical changesA chemical change produces one or more new substances, so simply reversing the physical conditions does not restore the original material and its properties.
Paper 1, Paper 2
A change in which new substances are formed because atoms are rearranged into different combinations.
Revise: Density and Mass in the Particle ModelA chemical change is different because atoms are rearranged into new combinations, producing new substances with different properties. Mass is still conserved in a closed system during a chemical reaction; the distinction is not whether mass is conserved, but whether new substances form. Simply reversing heating or cooling does not normally recover the starting materials from a chemical change.
When classifying a change, state what happens to the material: in a physical change the original substance remains and regains its original properties when the change is reversed; in a chemical change new substance(s) form.
Do not say that chemical changes fail to conserve mass. Mass is conserved in both physical and chemical changes when the whole closed system is considered.
To distinguish changes of state from chemical changes, state that no new substance forms. These changes of state can be reversed to recover the original material and its properties.
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