What Do Helmholtz and Gibbs Free Energy Mean in Thermodynamics?

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SUMMARY

Helmholtz free energy and Gibbs free energy are critical concepts in thermodynamics, defined through Legendre transformation. Gibbs free energy (G) indicates spontaneity in chemical processes at constant pressure and temperature, while Helmholtz free energy (A) applies to processes at constant volume and temperature. Both energies represent the available energy for doing work, with spontaneous processes occurring when these energies decrease, analogous to gravitational energy moving "downhill."

PREREQUISITES
  • Understanding of Legendre transformation in thermodynamics
  • Familiarity with the definitions of Enthalpy (H), Helmholtz free energy (A), and Gibbs free energy (G)
  • Knowledge of spontaneous processes in chemical reactions
  • Basic principles of thermodynamic systems at constant pressure and volume
NEXT STEPS
  • Explore the mathematical derivation of Helmholtz and Gibbs free energy equations
  • Study the implications of Gibbs free energy in chemical equilibrium
  • Investigate the applications of Helmholtz free energy in statistical mechanics
  • Learn about the relationship between free energy and entropy in thermodynamic processes
USEFUL FOR

Students and professionals in chemistry, physics, and engineering who seek to deepen their understanding of thermodynamic principles and their applications in spontaneous processes.

quantasham
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Hi guys,

We all know that Helmholtz free energy, Gibbs free energy and Enthalpy are defined by Legendre transformation.

For Enthalpy H=E+PV, I can understand it as the energy required to "displace the atmosphere" plus "creating the internal energy of system". What about Gibb free energy and Helmholtz free energy? What are their physical meaning?
 
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Hi quantasham! :smile:

Aren't they just the energy available for doing work?

So, for example, a chemical process is spontaneous at constant pressure and temperature if the Gibbs free energy would be decreased, and is spontaneous at constant volume and temperature if the Helmholtz free energy would be decreased.

So either Gibbs or Helmholtz free energy is like gravitational energy … a process will always go "downhill".
 

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