ECHE 311/SPRING 2015
Problem Set #7
FUGACITY
1. Estimate the fugacity of cyclohexene as a gas at 150oC and 50 bar, 150 bar, 300 bar and 2000
bar. Plot of f vs P and  vs P for cyclohexene at 150oC.
Hint: See example 4.1-1 in your handout.
2. Estimate the fugacity of liquid n-pentane at its normal-boiling-point temperature and 250 bar.
Hint: Step (1) Calculate the fugacity at the nbp by Eq.
P
  exp[ r ( B o    B1 )
Tr
Step (2) Calculate Vsat using Rackett Equation
Step (3) Use Eq.
V ( P  Pi
f i  isat Pisat exp sat
sat
)
RT
to calculate the pressure at 250 bar.
3. Prepare a plot of f vs P and  vs P for chloroform at 180 C for the pressure
range from 0 to 80 bar. At 180 C the vapor pressure of chloroform is 20.27 bar.
Assume
P
that Eq.   exp[ r ( B o    B1 ) is valid for the vapor phase and that the molar volume of
Tr
saturated liquid is given by Rackett Eq.
Hint: Use Rackett Eq to calculate Vsat
P
Calculate fugacity coefficients by Eq   exp[ r ( B o    B1 )
Tr
Use Eq.
V ( P  Pi
f i  isat Pisat exp sat
RT
sat
to calculate the fugacity from Psat and Vsat .
4. From data in the steam tables, determine a good estimate for f/fsat for liquid water at 150oC
and 150 bar, where fsat is the fugacity of saturated liquid at 150o C.
5. Steam at 9,000 kPa and 400oC undergoes an isothermal change of state to a pressure of 300
kPa. Determine the ratio of fugacity in the final state to that in the initial state.
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