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Thermodynamic potentials (Read 2615 times)
Gerrit-Jan Linker
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Thermodynamic potentials
10.04.09 at 19:03:50
 
Thermodynamic potentials
 
Thermodynamic potentials are useful for the description of non cyclic processes.
 
U
 
Internal Energy
U=energy needed to create the system
 
 
 
A=U-TS
 
Helmholtz free energy
A=energy needed to create a system minus the energy you can get from the environment.
 
H=U+pV
 
Enthaply
H=energy needed to create a system plus the work needed to make room for it
 
 
G=U+pV-TS
 
Gibbs free energy
G=total energy needed to create a system and make room for it minus the energy you can get from the environment
 
 

Method for calculating the Gibbs free energy:
G = Uref - TS  
S= -kBT ln z
z= ∑N exp(-un-uref)/kT; z is the partition function
 
The reference is arbitrary. If you chose another reference Uref, <U> and z will be different but G should be the same.
 
See also:
Partition function
http://www.oraxcel.com/cgi-bin/yabb2/YaBB.pl?num=1277736407
Chemical potential
http://www.oraxcel.com/cgi-bin/yabb2/YaBB.pl?num=1275213772/0#0
 
Reference:
Helmholtz Free Energy  
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/helmholtz.html
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« Last Edit: 20.11.14 at 13:10:52 by Gerrit-Jan Linker »  

Gerrit-Jan Linker
Linker IT Software
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Gerrit-Jan Linker
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Posts: 75
Thermodynamic energy definitions
Reply #1 - 27.05.10 at 09:07:39
 
Thermodynamic energy definitions
 
  • Free energy:
    The driving force for all physical processes.
    Free energy ∆A
    Free enthalpy ∆G       ∆G = ∆A + p∆V
     
  • Energy:
    The internal energy of the systems.
    Energy ∆E/∆U      
    Enthalpy ∆H             ∆H = ∆E + p∆V
     
  • Entropy:
    The number of realization possibilities
    Entropy ∆S
     
  • Helmholz / Gibbs equations
    ∆A = ∆E - T∆S
    ∆G = ∆H - T∆S
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Gerrit-Jan Linker
Linker IT Software
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