When cheese is heated and melted physical or chemical?

* No new substances are formed: The chemical composition of the cheese doesn't change when it melts. It's still made up of the same proteins, fats, and other components.

* The change is reversible: You can solidify the melted cheese by cooling it down, returning it to its original state.

* The change is primarily due to the change in state: The main change is the transition from a solid to a liquid due to the heat energy breaking the bonds holding the molecules together.

In contrast, a chemical change would involve:

* Formation of new substances with different chemical properties.

* The change being irreversible or difficult to reverse.

While some subtle chemical reactions might occur during the browning of cheese (like the Maillard reaction), the primary change during melting is physical.