Question

Why are changes of state physical changes?

Answer 1

Because changes of state do not involve the making and breaking of strong chemical bonds.

Explanation:

Chemical change is characterized by the making and breaking of strong chemical bonds, and the formation of new substances (I've said this many times before here; forgive me, I can never find the link when I need to use it). When card ice sublimes, or when water boils, the weaker intermolecular forces are disrupted, but the strong `C=O` or `O-H` bonds remain unbroken. Since the molecule remains inviolate, no chemical bonds are broken in a phase change, and the transition is properly regarded as a physical change. Capisce?