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

THERMODYNAMIC FEASIBILITY OF REACTIONS
The equilibrium constant K is a measure of the concentration of the products
formed at equilibrium. It is related by the equation ΔG 0 = - RT ln K. The more the value
of K, more will be the equilibrium conversion of products. When the value of ΔG < 0,
means the value of K should be very large. Hence ΔG is the measure of feasibility of a
chemical reaction.
i) If ΔG 0 < 0, there can be appreciable conversion of reactants in to products.
The more the –ve value, more will be the feasibility of the reaction
ii) If ΔG 0 is +ve but less than 10 000 k Cal / mol, the reaction is not feasible,
at atmosphere , may be feasible at any other pressure
iii) If ΔG 0 is greater than 10 000 kCal / mol the reaction is not at all feasible
under any condition.
Equilibrium Calculations ( Homogeneous gas Phase reactions):
aA (g) + bB (g) ↔ cC (g) + dD (g)
c
c y c c p
We have
f
Activity a E f
0
f
K
c d
a a
C D
a b
a A a
B
for gases,
0
as = p = 1 atmosphere: a = f
f = y but a f x p = y p
c c c c c c
c c c
K =
a y p
D D D D
a y p
A A A A
a y p
B B B B
A A A B B B A B A B A B
D y DD p
c D
x
y c yD x
c D
x
p p
y p y p y y p p
c + d - (a + b) n
()()()(P) y =()()()(P) where = activit y
y co efficient for gas phase
d c d c d c d c d
a b a b a b a b a b
K k k k k k k
y = mole fraction
= Fugacity Co efficient for gas phase
P = Total pressure