Reversible and Irreversible Expansion/Compression Processes: Summary

The answers to the ConcepTests are given below and will open in a separate window. 
Key points from this module:
  • Irreversible adiabatic expansion does less work than a reversible adiabatic expansion process that starts at the same conditions and ends at the same pressure. 
  • Irreversible adiabatic compression requires more work than a reversible adiabatic compression for a process that has the same initial conditions and the same final pressure.
  • The entropy always increases for an irreversible adiabatic process.
  • The final temperature is higher for an irreversible adiabatic process than for a reversible adiabatic process that starts at the same initial condition and ends at the same pressure.
  • A reversible process can readily go in the opposite direction with a slight change in driving force. 
From studying this module, you should now be able to:
  • Explain why a reversible adiabatic expansion generates more work than an irreversible adiabatic expansion between the same initial and final pressures.
  • Explain why a reversible compression requires less work than an irreversible compression between the same initial and final pressures.
  • Given three curves, identify which curve is reversible, which is irreversible, and which is isothermal for expansions and compressions on P-T, P-H, T-S, and H-S plots.
  • Determine whether a process is reversible or irreversible.

Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder