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Vapor pressure is where liquids are breaking off into the gas phase, below the boiling point. So is there a term where solids break off into the liquid phase, below the freezing point? Vapor pressure is to boiling point as ____ is to freezing point?

There is a equivalent vapor pressure for solids, which can be called sublimation pressure, where solids break off into the gas phase (like with dry ice), but I can't find 1 where solids break off into the liquid phase below the freezing point only when the vapor pressure equivalent surpasses a partial-pressure equivalent.

This is of course, my interpretation of "the other way around." I can't imagine the other way around being certain liquids solidify into solids above the freezing point. So for liquids, when the vapor pressure drops to equal the partial pressure, then condensation occurs - I can't imagine an equivalent where melting occurs above the freezing point (when the vapor pressure-equivalent surpasses a partial pressure-equivalent).

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    $\begingroup$ There is known overcooling of vapor and liquid, and overheating of liquid. But, unless I am mistaken, overheating of solid does not happen as it does not need seeding. // At freezing point, saturated vapor pressures over both liquid and solid are equal, with steeper curve for solids. $\endgroup$
    – Poutnik
    Sep 24 at 9:32
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One could say vapor pressure, again. When you have a solid and a liquid phase of a given material, each of these has its own equilibrium with the vapor. The favored phase at a given temperature and total applied pressure is the one with lower vapor pressure, since the other phase would "evaporate" enough to then favor condensation of the lower vapor-pressure phase. The freezing point is then the temperature where the vapor pressures are equal allowing both condensed phases to be in equilibrium with the same vapor.

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  • $\begingroup$ Some answers I got are: The broader term would be chemical potential of the solid vs liquid phases. For solids not much below their freezing point, the 1st few atomic layers on the surface can be disordered and partially mobile, resembling a liquid (but not the same as the actual liquid phase). However, the thermodynamic description of this region is not taken into account with regular thermodynamics, which considers the behavior of only the bulk. If you want to talk about the surface, you have to add extra terms to the potential energy of the molecules, in particular the surface energy. $\endgroup$ Oct 2 at 23:00

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