CER 126 : Thermodynamics of Materials May 13, 2022
Problem Set No. 3 Due : May 24, 2022
Name : ___________________________________________________
Answer the following ask questions.
1. You are responsible for the purchase of oxygen gas which, before use, will be stored at a
pressure of 200 atm at 300 K in a cylindrical vessel of diameter 0.2 m and height 2 m.
Would you prefer that the gas behaved ideally or as a van der Waals fluid? The van der
Waals constants for oxygen are a = 1.36 liters2 ・atm ・mole– 2 and b = 0.0318
liters/mole.
2. The virial equation of state for n -butane at 460 K is Z = 1 + A /V + B /V 2 , in which A =
– 265 cm3 /g ・mole and B = 30,250 cm6 /g ・mole2 . Calculate the work required to
reversibly compress 1 mole of n -butane from 50 to 100 atm at 460 K.
3. For sulfur dioxide, T cr = 430.7 K and P cr = 77.8 atm. Calculate
a. The critical van der Waals constants for the gas
b. The critical volume of van der Waals SO2
c. c. The pressure exerted by 1 mole of SO2 occupying a volume of 500 cm3 at 500
K. Compare this with the pressure which would be exerted by an ideal gas
occupying the same molar volume at the same temperature.
4. One hundred moles of hydrogen gas at 298 K are reversibly and isothermally compressed
from 30 to 10 liters. The van der Waals constants for hydrogen are a = 0.2461 liters2 ・
atm ・mole– 2 and b = 0.02668 liters/mole, and in the range of pressure 0– 1500 atm, the
virial equation for hydrogen is PV = RT (1 + 6.4 × 10– 4 P ). Calculate the work that
must be done on the system to effect the required change in volume and compare this
with the values that would be calculated assuming that (a) hydrogen behaves as a van der
Waals fluid and (b) hydrogen behaves as an ideal gas.
5. Using the virial equation of state for hydrogen at 298 K given in Problem 5, calculate
a. The fugacity of hydrogen at 500 atm and 298 K
b. The pressure at which the fugacity is twice the pressure
c. The change in the Gibbs free energy caused by a compression of 1 mole of hydrogen at
298 K from 1 to 500 atm
What is the magnitude of the contribution to (c) caused by the nonideality of hydrogen?