* Chemical property: A characteristic that describes how a substance interacts with other substances to form new substances. This involves changes in the chemical composition of the substance.

* Physical property: A characteristic that can be observed or measured without changing the substance's chemical composition.

When a substance reacts with acid, it undergoes a chemical change, forming new compounds. This change is not simply a physical alteration like changing its state (solid, liquid, gas) or appearance.

Example:

* Chemical property: Iron reacts with acid to form iron salts and hydrogen gas.

* Physical property: The density of iron is 7.87 g/cm³.

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