I am seeking some assistance with evaluating the entropy change for a real gas using BWRS-EOS. I have successfully accomplished this using Peng-Robinsons which will be used as a point for comparison. Any feedback or suggestions would be highly appreciated. Thank you in advanced.

Consider *Example 8.8. Enthalpy and entropy from the Peng-Robinson equation* - Introductory Chemical Engineering Thermodynamics by J. Richard Elliott. In this example a state change for Propane is studied. 

[![Example 8.8][1]][1]

The Python code below evaluates molar volume and enthalpy change successfully with V1 = 6047.7 cm3/mol, V2 = 1390.6 cm3/mol, dH = 7363.7 J/mol. However, entropy change is horribly incorrect, dS = -8.31 J/mol.

[https://pastebin.com/80w9npaT][2]

Entropy change has been evaluated as: 

$\Delta S = \Delta S_{ideal} + \Delta S_{real} = C_p * ln(\frac{T2}{T1})-R*ln(\frac{P2}{P1}) + (\Delta S_{departure2} - \Delta S_{departure1})$

This works very well for Peng-Robinsons EOS. I'm calculating an entropy change of 4.8J/mol vs 5.0J/mol as reported by J. Richard Elliott. However the result for BWRS is awful, and this appears to be due to the entropy departures which differ from PR-EOS by over 1000%. Summary of results in excel table below.

[![enter image description here][3]][3]

Entropy departure for BWRS is per K.E Starling Equation 10 in REPORT ORO-5249-2:

[![enter image description here][4]][4]

Can someone please verify my calculation for entropy departure for the BWRS equation of state?

Thank you so much

  [1]: https://i.sstatic.net/VFMkc.png
  [2]: https://pastebin.com/80w9npaT
  [3]: https://i.sstatic.net/VKFui.png
  [4]: https://i.sstatic.net/pYqwN.png