Which statement can be used to describe phase changes being driven by external conditions?

Which statement can be used to describe phase changes being driven by external conditions?

• A. Phase changes can be driven by changes in temperature and/or pressure.
• B. Phase changes can occur even without any change in temperature or pressure by adjusting volume?
• C. Phase changes occur only at an exact fixed temperature, regardless of pressure.
• D. Phase changes are random and not influenced by external conditions.

Answer: (B)

Phase changes are controlled by external conditions you can tune, especially temperature and pressure. The phase of a substance depends on where you are on a temperature–pressure map: changing the temperature at a given pressure can melt, freeze, or boil, and changing the pressure at a given temperature can shift the substance to a different phase as shown on phase diagrams. So the clearest way to describe how phase changes are driven is that they occur when temperature or pressure changes. The idea that a phase change can happen without any change in temperature or pressure by just adjusting volume is not accurate because adjusting volume typically changes the pressure (and, in turn, can affect the phase) rather than causing a phase change on its own. In other words, it's the changes in temperature or pressure that cross the boundaries between phases, not volume alone.

Phase changes are controlled by external conditions you can tune, especially temperature and pressure. The phase of a substance depends on where you are on a temperature–pressure map: changing the temperature at a given pressure can melt, freeze, or boil, and changing the pressure at a given temperature can shift the substance to a different phase as shown on phase diagrams. So the clearest way to describe how phase changes are driven is that they occur when temperature or pressure changes.

The idea that a phase change can happen without any change in temperature or pressure by just adjusting volume is not accurate because adjusting volume typically changes the pressure (and, in turn, can affect the phase) rather than causing a phase change on its own. In other words, it's the changes in temperature or pressure that cross the boundaries between phases, not volume alone.