What Do Helmholtz and Gibbs Free Energy Mean in Thermodynamics?

[quantasham]

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?

 

[tiny-tim]

Hi quantasham!

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".