Fugacity: It is derived from Latin, expressed as fleetness or escaping ...

For non ideal solutions f i i xik
i ----------(b)
Where i is an activity coefficient of component i.
Comparing equation (a) and (b)
f i
i Non ideal solution / Ideal solution
f
i
For both ideal and Non ideal solutions the fugacity of solution is given by
equation
f i
ln f xi
ln
x
ln
ln
xi i
i
Problem:
A terinary gas mixture contains 20mole% A 35mole% B and 45mole% C at 60 atm and
75 o C. The fugacity coefficients of A,B and C in this mixture are 0.7,, 0.6 and 0.9.
Calculate the fugacity of the mixture.
Solution:
ln x ln
x ln
x ln
A
A
ln 0.
2ln(
0.
7)
0.
35ln(
0.
6)
ln 0.
2975
0.
7426
f
, f =44.558atm
P
Gibbs Duhem Equation
B
B
c
c
0.
45ln(
0.
9)
Consider a multi component solution having ni moles of component I the property of
solution be M in terms of partial molar properties
t
nM nM
-----------------------(1).
M
i
Where n is the total no of moles of solution
Differentiating eq (1) we get
d( nm)
nid
M i
We know that
M idni
----------------------------(2)
, , n n P T f nM
1 2 ,