Which of the following best explains why cooking an egg is considered a chemical change?

• A. Cooking an egg involves melting, which is a physical change.
• B. Cooking an egg is reversible, so it is a physical change.
• C. Cooking an egg only changes its physical state from liquid to solid without altering its chemical composition.
• D. Cooking an egg causes the proteins to denature and form new chemical bonds, resulting in a new substance.

Answer: (D)

Verified step by step guidance

1. Understand the difference between physical and chemical changes: Physical changes affect the form of a substance but not its chemical composition, while chemical changes result in the formation of new substances with different chemical properties.
2. Analyze what happens when an egg is cooked: The heat causes the proteins in the egg to denature, meaning their three-dimensional structures unfold and then re-bond in new ways.
3. Recognize that this denaturation and re-bonding of proteins changes the chemical structure of the egg, creating new substances rather than just changing its physical state.
4. Note that melting or changes in physical state (like liquid to solid) do not involve breaking or forming chemical bonds, so they are physical changes, not chemical changes.
5. Conclude that because cooking an egg results in new chemical bonds and new substances, it is classified as a chemical change.