Final answer:
Boiling water to form bubbles is a physical change, where water changes from a liquid to a gas state without any bonds being broken or formed within the water molecules.
Step-by-step explanation:
No, your brother is not correct. The bubbles that you see forming at the bottom of the pot when boiling water are not due to a chemical change but rather a physical change. When water boils, the heat energy is causing the water molecules to move more rapidly, eventually changing from a liquid to a gas state, known as water vapor. This phase change does not involve breaking or forming of bonds within the water molecules themselves (H2O remains H2O), which would be required for a chemical change.
Chemical changes involve the forming and breaking of chemical bonds, resulting in new substances with different properties. A classic example of a chemical change is the burning of wax, which produces water and carbon dioxide as new chemicals with distinct properties from those of the original substance. However, in the case of boiling water for noodles, only the physical state of water changes from liquid to gas without altering the chemical structure. Thus, the bubbles you see are simply water vapor.