How can phase changes be reversed?

How can phase changes be reversed?

• A. By changing the chemical composition of the substance.
• B. By changing temperature and/or pressure to reverse the phase change.
• C. By changing temperature to reduce its volume.
• D. By adding a catalyst.

Answer: (B)

Phase changes happen when temperature and pressure move a substance across the boundaries between solid, liquid, and gas. To reverse a phase change, you change temperature and/or pressure so the system returns to the previous phase region on the phase diagram. So by adjusting heat (temperature) and pressure, you can undo the change and go back to the original state. The other ideas don’t fit because changing composition creates a different material with its own phases, catalysts affect rates rather than phase boundaries, and reducing volume alone doesn’t guarantee crossing back to the original phase.

Phase changes happen when temperature and pressure move a substance across the boundaries between solid, liquid, and gas. To reverse a phase change, you change temperature and/or pressure so the system returns to the previous phase region on the phase diagram. So by adjusting heat (temperature) and pressure, you can undo the change and go back to the original state. The other ideas don’t fit because changing composition creates a different material with its own phases, catalysts affect rates rather than phase boundaries, and reducing volume alone doesn’t guarantee crossing back to the original phase.