# Calculating the partial pressure of pure Zinc over a solution? over

1. Dec 3, 2011

### billboard

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=
lnaB
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. Dec 3, 2011

### Staff: Mentor

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