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Increasing pressure does what to temperature?

  1. Dec 16, 2011 #1
    1. The problem statement, all variables and given/known data

    A certain substance exists in two phases at equilibrium at Temp T1 and pressure P1. One phase α is a crystalline solid (density 0.531 g/cm^3) while the other phase β is an amorphous glass (density 0.510 g/cm^3).

    a) If the external pressure is increased, will the temp at which the α→β conversion takes place increase or decrease?

    b) If the external pressure is increased isothermally, what will happen?


    2. Relevant equations

    density=mass/volume

    dP/dT = ΔHvap/TΔV ??

    3. The attempt at a solution


    a) If the external pressure is increased, will the temp at which the α→β conversion takes place increase or decrease?

    I know that the curve between the two phases is where the two phases exist at equilibrium and that it is dP/dT and that relates to density (which is 1/V).

    I want to say that if you increase the pressure, the temp of the conversion will increase but I am assuming that the curve looks like that of a water phase diagram. How do I determine if it increases or decreases by using the density?

    b) If the external pressure is increased isothermally, what will happen?

    Increasing pressure isothermally means that the temperature stays constant. So we will end up with only one phase (I'm not sure which, the α or the β. I feel like this might also have something to do with the density.)
     
  2. jcsd
  3. Dec 17, 2011 #2

    Borek

    User Avatar

    Staff: Mentor

    IMHO For the first part LeChatelier's principle is enough. When pressure goes up, system tries to occupy lower density, so the higher density phase becomes favored. Now just try to apply this line of thinking to the question.
     
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