Ben asked in Science & MathematicsChemistry · 1 month ago

Why does ice have a higher vapor pressure than liquid water at temperatures above 0 degrees C? ?

At temperatures >0C and after the system in the photo reaches equilibrium, only liquid water will remain in the right cell. This is because, at this temperature, the solid requires a higher pressure than the liquid does to be in equilibrium with the vapor. Thus, as vapor is released from the solid to try to achieve equilibrium, the liquid will absorb vapor in an attempt to reduce the vapor pressure to its equilibrium value.

 I understand the above concept. However, what I don't understand is why the solid has a higher vapor pressure than the liquid at this temperature at all. Does it have to do with the molecules being farther apart from one another in the lattice structure? The photo and some of this text was taken from Zumdahl & Zumdahl 9th ed. 

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2 Answers

  • Dr W
    Lv 7
    1 month ago

    You misinterpreted that entire section (10.8).  Re-read it!  Note that the P-T curves are extrapolated for liquid H2O below 0°C and for solid water (ice) above 0°C.  Pay attention to the text that describes the phase changes from solid to liquid and from liquid to solid.   Note the wording "In fact, no solid can exist under these conditions." etc.  and which phase is present.

    What Zumdahl is describing is a setup where liquid and solid are initially placed into a setup that is connected only by vapor phase.  And after some time, only 1 phase exists.  

  • 1 month ago

    I'm not sure that information in 100% correct. You will note that the VP info for ice (shown in previous diagram) was extrapolated and of course water is supercooled. Getting ice to superheat is not a trivial task. Then trying to measure vapor pressure....good like finding that information. If you are in college, ask the professor to provide some sources. If you are in high school AP does not require that bit of stuff, so if you are learning it ask your teacher to explain which they probably can't.

    I think the idea is to more understand VP equilibrium between 2 phases instead o the idea of VP of supercooled water and superheated ice.

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