Which factor can reverse a phase change?

Which factor can reverse a phase change?

• A. Only temperature can reverse a phase change.
• B. Only pressure can reverse a phase change.
• C. Adding a catalyst can reverse a phase change.
• D. Changing temperature and/or pressure can reverse a phase change.

Answer: (D)

Phase stability is determined by temperature and pressure. A phase change occurs when you cross a boundary in the temperature–pressure space that separates solid, liquid, and gas. To reverse a phase change, you move back across that boundary by changing either temperature or pressure (or both). For example, cooling liquid water below 0°C at 1 atm reforms solid ice, and increasing pressure on a gas at a given temperature can condense it back to a liquid. A catalyst doesn’t alter these thermodynamic conditions; it only speeds up processes. So the factor that can reverse a phase change is changing temperature and/or pressure.

Phase stability is determined by temperature and pressure. A phase change occurs when you cross a boundary in the temperature–pressure space that separates solid, liquid, and gas. To reverse a phase change, you move back across that boundary by changing either temperature or pressure (or both). For example, cooling liquid water below 0°C at 1 atm reforms solid ice, and increasing pressure on a gas at a given temperature can condense it back to a liquid. A catalyst doesn’t alter these thermodynamic conditions; it only speeds up processes. So the factor that can reverse a phase change is changing temperature and/or pressure.