# Gibbs free energy

1. Dec 13, 2011

### cragar

I don't think I completely understand what Gibbs energy is, Is it the work you can get out of a system at fixed Temperature and pressure. Does any one have another angle on it cause It seems weird to me.

2. Dec 14, 2011

### Andy Resnick

The Gibbs free energy is the total energy available to a system, G = H-TS, and is used instead of other free energies such as the Helmholtz free energy (I think there are others as well) when the system undergoes isothermal and isobaric processes. The Helmholtz free energy is more applicable for isothermal and isochoric processes.

Processes that result in a change in the Gibbs free energy ΔG = ΔH-TΔS are classified as "spontaneous" or not depending on the sign of ΔG.

3. Dec 14, 2011

### cragar

$G=\sum_i N_i \mu_i$ i.e. it can be expressed in terms of the chemical potentials of the components.