Questions: Cooking as Chemical Change

Question 1

You crack a raw egg into a hot pan. The clear, runny egg white becomes solid and white. What kind of change is this?

• A. Physical change — the egg just melted into a different shape
• B. Reversible change — if you cool the egg, it will become runny again
• C. Chemical change — heat caused the egg proteins to form new bonds, creating a new substance with different properties
• D. No change — the egg was always white

Answer: (C)

Cooking an egg is a chemical change. The heat breaks apart the protein structures in the egg and causes them to reform in a completely new arrangement. The result — a firm, white, opaque solid — has entirely different properties from the raw egg. You cannot reverse this by cooling the egg.

Question 2

If you cool a baked cake back down to room temperature, it will turn back into raw batter.

• T. True
• F. False

Answer: False

False. Baking a cake is an irreversible chemical change. The heat caused the flour, eggs, sugar, and other ingredients to react and form new substances. Cooling the cake just makes it a cold cake — it does not reverse the chemical reactions that occurred during baking.

Question 3

Why is cooking an egg a chemical change but melting butter a physical change?

Model answer: Cooking an egg creates new substances — the proteins change permanently and cannot go back to their raw form. Melting butter just changes its state from solid to liquid without creating new substances. You can re-solidify butter by cooling it, but you cannot uncook an egg.

The key difference is whether new substances form. Melted butter is still butter — same substance, different state. A cooked egg is a different substance entirely from a raw egg — different color, texture, and properties. The chemical bonds in the egg proteins were broken and reformed into a new arrangement.