text: *Thermodynamics, University of Colorado-Boulder, 2011
  **[https://www.youtube.com/watch?v=fkqmf_QR4Yg Introduction to fugacity: Where did it come from?]
  **[https://www.youtube.com/watch?v=AMBoLiQJMFQ What is fugacity?]
  **[https://www.youtube.com/watch?v=OZFB48wVtjw What is fugacity in mixtures?]