* New Substances Are Formed: When you cook food, you apply heat which alters the chemical composition of the ingredients. Proteins change structure (denature), starches break down into simpler sugars, fats melt and potentially break down, and water evaporates. These are all examples of new substances being formed.

* Irreversible: You can't easily reverse the cooking process to get back the original ingredients. For example, you can't uncook a boiled egg.

* Chemical Reactions: Cooking involves chemical reactions, like the Maillard reaction (which gives food its brown color and savory flavor) and the breakdown of carbohydrates.

Examples:

* Baking a cake: Flour, sugar, eggs, and butter are combined and transformed into a cake through chemical reactions.

* Roasting vegetables: Heat causes the vegetables to soften and change color due to chemical changes within their cells.

* Boiling pasta: The heat breaks down the starch molecules in the pasta, changing its texture and making it digestible.

Physical Changes:

In contrast, physical changes involve only changes in the form or appearance of a substance, not its chemical makeup. Examples of physical changes include:

* Cutting vegetables: You're changing the shape of the vegetable, but not its chemical composition.

* Freezing water: Water changes from a liquid to a solid, but it's still H2O.

* Melting butter: The butter changes from a solid to a liquid, but it's still the same chemical compound.