Page 95 - Modeling of Chemical Kinetics and Reactor Design

Thermodynamics of Chemical Reactions 65
 ∑ υµ 

−

= exp  i i  = K (2-33)
 RT 


The right side is the equilibrium constant, K. The left side contains
the fugacities of the reactants in the mixture at the equilibrium com-
position. For gases, the right side is independent of pressure and
composition and is equivalent to

ag + bg − cg − dg o D (2-34)
o
o
o
C
B
A
o
where g is the specific Gibbs function of pure A at the standard state
A
conditions, that is
g = h o A − Ts o A (2-35)
o
A
IDEAL GAS MIXTURES
For an ideal gas mixture, a = p , which is expressed as
i
i
c
p • p d
C D = K
a
p • p b B p (2-36)
A
where p is the partial pressure. This is related to the total pressure as
the total pressure, P , multiplied by the mole fraction of the component
T
in the mixture. That is:

p = y P (2-37)
i i T
Substituting Equation 2-37 into Equation 2-36 yields

c
y • y d D P ( cda b) = K
+− −
C
a
y • y b B T p (2-38)
A
REAL GASES—IDEAL GASEOUS SOLUTION

In many cases, the assumption of ideal gases is not justified and it
will be essential to determine fugacities. An example of such reactions