Final answer:
A physical change is when matter changes its form or properties without changing its chemical identity, such as melting ice or evaporating water.
Step-by-step explanation:
A physical change is a type of change in which the form of matter is altered but its identity remains the same. For example, when an ice cube melts, it goes from a solid to a liquid (Figure 1.2.3); this change alters its shape and allows it to flow, yet the chemical composition of water (H₂O) does not change. Another instance is when water vaporizes; the temperature and energy of water molecules increase leading to evaporation, turning liquid water into water vapor (H₂O (l) → H₂O (g)), without altering the molecular structure.
Sorting a mixture of pennies and nickels changes the arrangement of the coins without changing their properties. Similarly, tearing a piece of paper changes its shape and size, but it remains paper. These examples show that during a physical change, the arrangement of particles may change, but the mass, number of atoms, and number of molecules stay the same.