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

H T T T
0
H
T
0 2
H298
0 2
d
H T T
dT
298
2 3
OR in general
o
2 3
H T
T T I
P
0 2
H C dT T T dT
=
2 3
2 3
T T T I
A chemical reaction proceeds in the direction of decreasing free energy.The sum of the
free energies of the reactants should be more than the sum of energies of products. For a
reaction to take place
G G G or G 0
Re action Re action
products reaction
Therefore ΔG should be less than zero for a reaction to occur. When equilibrium is
reached free energies of the reactants equal free energies of products,. Therefore the
criterion for reaction equilibrium is ΔG = 0
ΔGReaction Calculation: Consider the reaction aA + bB ↔ cC + dD
Let GA, GB, GC , and GD be the partial molar free energies of A,B,C, and D in the
reaction mixture.
2 3
o
2 3
H T
T T I
f f
G G RT ln but a the activity of A
0 A A
A A 0
fA 0
fA
A
G G RT lna
A
0
A A
G G RT lna
B
0
B B
G G RT lna
C
0
C C
G G RT lna
D
0
D D