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Homework Help: Calculating the partial pressure of pure Zinc over a solution? over

  1. Dec 3, 2011 #1
    1. The problem statement, all variables and given/known data

    The activity coefficient of zinc in liquid brass is given (in joules) by the following equation for
    temperatures 1000-1500 K:
    RT ln γZn = -38,300 x2Cu

    where xCu is the mole fraction of copper. Calculate the partial pressure of pure zinc PZn over a
    solution of 60 mol% copper and 40 mol % zinc at 1200 K. The vapor pressure of pure zinc is
    1.17 atm at 1200 K.

    2. Relevant equations

    For dilute solutions: xs: mole fraction of solvent, xu: mole fraction of solute,
    The vapour pressure of the solvent= Ps= P(pure)xs=P(pure)(1-xu) where is P(pure)=vapour pressure of the pure solvent.

    Gibbs-Duhem Relationship=
    lnaA= - ∫ xB/ xa * d(lnaB)

    3. The attempt at a solution

    d (lnγA)= - XB/XA * d(lnγB) applying Gibbs-Duhem rel. in the form of this eqnn:
    dxcu= -dXzn
    lnγCu= - 38.300/ RT * X^2Zn

    How can i get the partial pressure of pure zinc PZn?

    Thanks! :)
  2. jcsd
  3. Dec 3, 2011 #2


    User Avatar

    Staff: Mentor

    Activity coefficient in Joules? Shouldn't it be unitless?
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