1. [ ] Unit 3 – Real & Ideal Gases Non-ideality of gases - Fugacity
Can generalize for a real gas ( )
.... 1 2 3 + = P T B RT V o f G , ln Þ
The thermodynamic function fugacity.
Note: f (P,T)  P as P  0 [ ]
......
exp ( ) o T P RT G V ln , + = Þ ÷ ø ö ç è æ
Standard molar Gibbs energy
1 bar
Gibbs energy must be taken relative to some standard state
Standard state of real gas is taken to be the corresponding ideal gas at 1 bar
i.e. must “adjust” the real gas to ideal behavior
Real gas (T,P)
Ideal gas (T,P)
Real gas (T, P  0) = Ideal gas (T, P  0)
G1
G2
G3 o P f RT dP V G ln ' 1 - = ò ÷ ø ö ç è æ D

2. P f = g 1 ln dP P Z ò - = g Fugacity coefficient
Ideal gas,  = 1. Fugacity coefficient measures extent of non-ideality ' 1 ln dP P Z ò - = g
(Z-1) / P
P (bar)  1
P (bar)
ideal
Real