The chemical formula H₂O represents water, which is a substance. Substances are physical things, not changes.

Here's why:

* Chemical formula: H₂O describes the composition of water molecules, telling us it contains two hydrogen atoms and one oxygen atom.

* Physical property: The formula is a physical property of water, just like its color, density, or boiling point.

* Chemical change: A chemical change would involve water being transformed into something else, like breaking down into hydrogen and oxygen gas (2H₂O → 2H₂ + O₂).

So, to answer your question directly: H₂O is a physical representation of a substance, not a change.