* Change in chemical composition: When wax hardens, the long hydrocarbon chains in the wax molecules become more tightly packed together. This change in structure results in a change in the chemical composition of the wax.

* Irreversible process: Hardening is generally an irreversible process. You can't simply melt the hardened wax and have it return to its original state. The process of hardening introduces new chemical bonds and changes the overall structure of the wax.

* New properties: Hardened wax has different properties than liquid wax. It's more solid, has a higher melting point, and may be more brittle.

Example: Candle wax is a good example. The liquid wax cools and hardens, changing its physical state and its chemical composition. The process can't be reversed without adding heat to melt the wax again.

Therefore, the hardening of wax is a chemical change because it involves a change in the chemical composition and properties of the wax.