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Quick question about Gibbs free energy

  1. Jun 2, 2013 #1
    In the expression defining Gibbs free energy,
    G = U - TS +pV,
    are T and p the temperature and pressure of the environment, or of the system itself? Or is it a requirement that the system has the same temperature and pressure as the environment for the Gibbs free energy to be defined?
     
  2. jcsd
  3. Jun 2, 2013 #2
    T and p describe the system. For a system in thermal equilibirum and mechanical equilibrium with the environment - consider the system surrounded by heat and pressure reservoirs - the Gibbs free energy is at its minimum value.
     
  4. Jun 2, 2013 #3
    Thanks.
    Part of the reason for my confusion is this page:
    http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/helmholtz.html
    Seems to me that the "work to give the system final volume V at constant pressure p" should be equal to pV where p is the pressure from the surroundings?
     
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