* No new substances are formed: When salt (NaCl) dissolves in water, the sodium (Na+) and chloride (Cl-) ions separate and become surrounded by water molecules. The salt itself doesn't change its chemical composition; it simply breaks down into its constituent ions.

* The change is reversible: You can easily recover the salt by evaporating the water. The ions recombine to form solid salt again.

Key characteristics of a chemical change:

* New substances are formed.

* The change is usually irreversible or difficult to reverse.

* There is a change in energy (heat released or absorbed).

Since dissolving salt in water doesn't meet these criteria, it's classified as a physical change.