pl = plo
+ RT
In Ylxl
where p l o is the reference chemical potential taken as that of the pure liquid, 71 is the activity coefficient of component 1, all a t the temperature T. Substituting eq 7 into eq 6 and expressing the activity. coefficient by the van Laar equation
A(l - Xi)' [(I - xl) Qxll' where Q = A / B , we have -1 - 2AQ(1 - xi) (9) Qx1I3= x i [(l - xl) This equation presents two roots in the composition range 0 < XI < 1,if the following conditions are obeyed In y i =
+
+
Q21
(10) (11)
With the symbol [ Q ] we indicate the integer part of Q, i.e., the integer number n which verifies the relation n 5 Q
