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

Fugacity coefficient ( ) : Fugacity coefficient ids defined as the ratio of fugacity of a
component to its pressure.
f
P
Is the measure of non ideal behavior of the gas.
Standard State: Pure gases, solids and liquids at temperature of 298k at 1 atmosphere are
said to exist at standard condition. The property at this condition are known as standard
state property and is denoted by subscript’o’.
o
G = Standard Gibbs free energy
o
f = Standard fugacity
Estimation of fugacity for gases
I method
dG VdP SdT
For Isothermal conditions
dG VdP
from equation (2)
RTd ln f VdP
V
d ln f dP
RT
Integrating the above equation with the limits 0 to f and pressure 1 to P
d ln f
P
1
V
RT
dP
Lower limit is taken as P =1 atm
At 1 atm assuming the gases expected to behave ideally
P
1
ln f VdP
RT 1
if PVT relations are known , we can find fugacity at any temperature and pressure