Changes of state, such as melting, freezing, boiling, and condensation, are considered physical changes because they alter the form of a substance but not its chemical composition. For example, when ice melts into water, the molecules move from a solid state to a liquid state, but the chemical structure of water (H2O) remains the same.
During these changes, energy is either absorbed or released, which leads to an increase or decrease in the motion of particles. However, the fundamental identity of the substance does not change. This distinguishes physical changes from chemical changes, where substances are transformed into different substances through chemical reactions. In summary, the changes of state are termed physical changes because they involve transitions that affect only the physical state and not the actual chemical makeup of the material.