Final answer:
Boiling water is a physical change because the molecular structure of water remains H₂O and the process can be reversed; no new substances are formed and no chemical bonds are broken.
Step-by-step explanation:
Boiling water is considered a physical change because it involves a change in the state of matter from liquid to gas without altering the chemical composition of the substance. When water boils, the molecular structure of water does not change; rather, the molecules gain enough energy to overcome the attractive forces that hold them together in the liquid state, allowing them to spread apart and form water vapor. This process can be reversed by condensing the water vapor back into liquid water, confirming its status as a physical change.
Phase changes such as boiling or melting are classic examples of physical changes because they involve changes in energy and states of matter without any alteration to the chemical identity of the substance. Therefore, during the boiling of water, the water remains H₂O throughout the process, adhering to the principle that physical changes do not break bonds within molecules or form new substances.