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Questions Regarding Effect of Nucleation in Phase Change

  1. Oct 16, 2014 #1
    1. Is nucleation a phenomenon that occurs in all phase change (freezing/melting, evaporation/condensation)?

    2. I've always read evaporation/condensation described as a liquid-vapour interface phenomenon (water molecules going entering-leaving the interface at equal rates in equilibrium). If evaporation/condensation require nucleation, doesn't this mean that if I lower the temperature of a liquid-vapour system at equilibrium, condensation will occur on the nucleation site in the chamber (and if no nucleation sites are present the system will supersaturate) as opposed just going into the liquid?

    3. This is more of a general question about free energy. When there is a phase disequilibrium, I get that the spontaneous process is one where dG < 0. However, since nucleation (and other processes) requires an temporary rise in free energy (to create the nucleus), why do we use the criterion that dG < 0 (a differential) as opposed to ΔG (between initial and final state)?

    Thank you
     
  2. jcsd
  3. Oct 21, 2014 #2
    Thanks for the post! Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
     
  4. Oct 27, 2014 #3
    1/2. I'm basically wondering if nucleation is a requirement for phase change. For instance, when liquid water is at equilibrium with its vapour, does individual molecules simply enter/leave the interface, or does nuclei have to form to induce the phase change?

    3. Thermodynamically, I'm wondering what the difference between dG and ΔG is and why we use dG < 0 to describe whether phase change is spontaneous, when by nucleation theory phase change requires free energy to increase (to form the nucleus) before decreasing.
     
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