* Physical Changes: Involve changes in the form or appearance of a substance, but not its chemical composition. The molecules themselves remain the same. Examples include melting, freezing, boiling, and sublimation.

* Chemical Changes: Involve the formation of new substances with different chemical compositions. The molecules are rearranged, and new bonds are formed or broken. Examples include burning, rusting, and cooking.

Melting fat is simply changing its state from solid to liquid. The molecules of fat (triglycerides) remain the same, just rearranged in a more fluid arrangement. It's reversible too - you can solidify the fat again by cooling it down.

Important Note: While melting is a physical change, cooking with fat involves some chemical changes. Heat can break down fat molecules, creating different compounds and flavors.