AP Chemistry Practice Exam Prep: Comprehensive Practice Test & Study Guide

The melting of ice is an example of a physical change because it involves a change in state from solid to liquid without altering the chemical composition of the substance. During this process, the water molecules in ice gain energy and move more freely, but the identity of the substance remains as H₂O. Physical changes are characterized by changes that can be easily reversed and do not involve the creation of new substances.

In contrast, burning of wood and rusting of iron are chemical changes since they result in the formation of new substances: ash and gases from burning, and iron oxide from rusting. Digestion of food is also a chemical change as it involves breaking down food into different chemical components, making it a more complex transformation than merely melting or freezing. This distinction reinforces why melting ice clearly illustrates a physical change.