Ground state elevation for phase transition I have a question about the illustration from chem.libretexts.org:


the ground states of the liquid and gas are offset from that of the previous state by the heats of fusion and vaporization, respectively.

Why does the change in enthalpy increase the ground state energy?
I would be very grateful if someone can help me with this problem. I have been struggling with it for five days, but Google could not help me.
P.S. My question mark does not work.
In order to make the phase transition, you need to supply your sample molecules with an additional amount of kinetic energy (i.e., the heat of fusion or vaporization) to overcome their intermolecular bonding. This however means that after the transition, your system contains more internal energy than before. That additional energy is encoded in the vertical offset on the energy scale.

Note that if you look at each phase on its own, you could set the their ground states as the zero point on your energy scale. However, if you want to compare the system among different phases, then you need to take that offset into account. Otherwise you'd assume that your system can change from solid to liquid to gas without any effort.