Interactive Self-Study Module: Departure Functions
Department of Chemical and Biological Engineering, University of Colorado Boulder 

This module uses a screencast and an interactive simulation to explain how to use an equation of state or steam tables to calculate the departure function. It then provides example problems  to allow the user to test themselves. We suggest using the learning resources in the following order:

  1. Attempt to answer the multiple choice ConcepTest and solve the example problem before watching the screencasts or working with the simulations.
  2. Watch the screencast that explains the enthalpy departure function. 
  3. Use the interactive simulation to compare real and ideal gas enthalpies and entropies.
  4. Try to solve the two example problems before watching the solutions in the screencasts.
  5. Answer the ConcepTests.
        Real gases can be modelled by calculating the differences from ideal gases of state functions.
        This module is intended for a Thermodynamics course. 

Before studying this module, you should:

  • Calculate changes in properties for ideal gases
  • Calculate internal energy and enthalpy changes for ideal gases. 
  • Calculate entropy changes for ideal gases. 
  • Apply the concept of state functions to devise a pathway to calculate property changes of real gases. 
  • Know how to use steam tables

After studying this module, you should be able to:
  1. Explain what a departure function is.
  2. Calculate U, H, S, and G using the PVT relations in the EOS spreadsheet.
  3. Calculate changes in state variables using departure functions and ideal gas heat capacities. 
  4. Explain why ideal gas heat capacities can be used for real fluid calculations. 
  5. Use the departure function approach to solve first and second law problems for real fluids.