In Vapor-Liquid Equilibrium, it is my understanding that molecules exchange between the gas and liquid continuously; even when no difference in temperature or partial pressure exists.

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Regarding Solid-Liquid Equilibrium; is there a similar continuous exchange of molecules? For example on a single crystal of ice submerged in pure water at perfect and constant 0°C, will molecules on the surface of this crystal exchange with the liquid? In the past I have assumed this to be the case, but now realize I have not seen a reference that explicitly details this like is common for vapor-liquid equilibrium. Are there any references that calculate the rate at which this occurs? Side question, is there also a continuous exchange for solid-gas equilibrium?

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    $\begingroup$ Yes, and yes. All solids have some vapor pressure, and (often negligible) solubility. $\endgroup$
    – Mithoron
    Jun 5, 2022 at 20:48
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    $\begingroup$ Generally, molecules/atoms/ions have no means for awareness the system is in equilibrium, being "instructed to do nothing". Additionally, they do not have temperature. A single kinetic energy value belongs to a wide range of possible system temperatures, so they are changing a phase at will. $\endgroup$
    – Poutnik
    Jun 6, 2022 at 8:20
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    $\begingroup$ Your question was already answered chemistry.stackexchange.com/questions/73344/… $\endgroup$ Jun 8, 2022 at 3:55
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    $\begingroup$ Does this answer your question? Proof of Dynamic Nature of Equilibrium $\endgroup$ Jun 8, 2022 at 3:55

1 Answer 1


Even two solids in contact may exchange atoms, such as gold in contact with lead. Accidental cold-welding is a serious problem in space technology, in particular.

You can prove to yourself that ice/water, in equilibrium, exchanges molecules: immerse an ice-cube on a string in water at 0°C, and the cube will slowly change shape. "No chemist ever observes the same ice cube twice..." as Heraclitus or Heisenberg stated (I'm not certain).


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