What are the key signs that a physical change involving states of matter has occurred?

• A. A change in state (solids, liquids, gases) with energy transfer but no new substances formed.
• B. A new substance formed.
• C. A color change alone indicates a chemical reaction.
• D. Mass disappears.

Answer: (A)

Phase changes are changes between solid, liquid, and gas that involve energy transfer but keep the substance's identity. When heat is added or removed, particles gain or lose energy, allowing them to rearrange into a different state—melting, freezing, boiling, condensation, or sublimation—without changing what the material is. Because no new chemical bonds form, the same substance remains, so no new substance is produced. That combination—change of state with energy transfer and no new substance formed—best captures what signals a physical change in states of matter. If a new substance were formed, that would point to a chemical change; a color change alone isn’t a definitive indicator of a phase change, and mass disappearing would violate the conservation of mass.