* Chemical Composition Changes: The heat from cooking alters the chemical makeup of the proteins in the steak.

* Maillard Reaction: This is a key chemical reaction that gives steak its browned color and savory flavor. It involves the interaction of sugars and amino acids in the meat.

* Protein Denaturation: Heat causes the proteins in the steak to unfold and change their structure. This is why cooked steak is firmer than raw steak.

* Breakdown of Fat: Fat in the steak melts and renders, contributing to the flavor and tenderness.

* Irreversible Change: Once cooked, the steak cannot be easily returned to its raw state. The chemical changes are permanent.

In contrast, a physical change would be:

* Cutting the steak: This alters the shape but doesn't change the steak's chemical makeup.

* Freezing the steak: This changes its state of matter (solid to frozen) but not its chemical composition.