
Perturbation Theories for Simple Fluid Mixtures 187
7.4.2 EXTENSION TO MIXTURES OF FREE ENERGY PERTURBATION THEORIES
The extension to mixtures of some of the perturbation theories based on the series
expansion of the free energy analyzed in Chapter 6 is straightforward. For the ref-
erence system, we may choose single- or multi-component systems. Thus, using
a single-component HS reference system, Equation 6.39 for the free energy in the
first-orderperturbation theory for simple fluids, for mixtures transforms into (Leonard
et al. 1970)
F
Nk
B
T
=
F
0
Nk
B
T
+
i
x
i
ln x
i
+2πβρ
i,j
x
i
x
j
∞
σ
ij
u
ij
(
r
)
g
0
(
r
)
r
2
dr, (7.49)
where subscript 0 refers to a single-component fluid ...