Is mixing alcohol with water a chemical change or a physical change?

Sort of both.

Looking first at a liquid of pure methanol, the researchers observed the presence of rings and chains made of six to eight methanol molecules. When they mixed methanol and water, they found that the chains connected with water molecules to form larger water/methanol clusters.

These clusters are very stable, because of the strong chemical bonds that hold them together. But the molecules don't like to form big, ordered chunks - they tend to prefer smaller arrangements. The flow of molecules in a liquid encourages bonds between alcohol and water to quickly form and disappear. So the weak pull of water loses against the stronger pull of the bonds within alcohol, but the constant tug keeps the alcohol from forming big chunks.

So nature discourages the formation of more clusters in the liquid, and this can explain why alcohol and water don't like to mix.


https://www.quora.com/What-happens-when-ethanol-is-mixed-with-water