Which of the following is true about phase changes?

All three are true, but the third is conditionally true. If pressure and temperature are both changing in opposite directions, you can manipulate how they change to cancel each other out (but who wants that?).

• Changing the temperature will eventually go past a boiling point #T_b# or freezing point #T_f#, and a phase change will occur.

where Chemical Potential is #mu = barG# (molar Gibbs' Free Energy) and the chemical potential decreases as the temperature increases so as to minimize the amount of energy in the system.

Chemical Potential can be treated just like "energy levels".

Technically, the slope is #((deltamu)/(deltaT))_P = ((deltabarG)/(deltaT))_P = -S#, which shows that the magnitude of the entropy increases as the density of the substance decreases (solid #-># liquid #-># gas).

It's assumed that the pressure is held constant, hence the subscript #P#.

• Changing the pressure around a substance will compress it or allow it to expand and change phase too.

where pressure is #P#. As pressure increases , the substance compresses more and it eventually transitions into a liquid (smaller molar volume, #barV#, hence flatter slope), then solid, etc.

It's assumed that the temperature is held constant, hence the subscript #T#. #P_B# is pressure while changing phase from gas to liquid.

• And of course, if either one affects the phase, doing both in the same direction will make it happen more easily. If they are in opposite directions then it will depend on the intensity of each one.