Final answer:
Boiling at 450 degrees Celsius is a physical change because the substance's chemical composition does not change; it merely transitions from a liquid to a gas phase.
Step-by-step explanation:
Boiling at 450 degrees Celsius is a physical change. During the boiling process, no chemical bonds are broken or formed, and the substance undergoing the phase change retains its identity. The example of water boiling can be represented by the chemical notation H₂O (l) → H₂O (g), where (l) stands for liquid and (g) stands for gas. This notation indicates that water transitions from its liquid phase to its gas phase while remaining chemically unchanged.
By contrast, a chemical change involves a transformation where new substances are produced. An example of a chemical change is rust forming on a nail, represented by the reaction Fe + O₂ → Fe₂O₃, where iron (Fe) reacts with oxygen (O₂) in the air to produce iron oxide (Fe₂O₃), also known as rust, which has different properties than the original substances.