Gibbs Free Energy Change (constant pressure and temperature)

The Gibbs Free Energy function^[1], ΔG = ΔH - TΔS, calculates the maximum useful energy obtainable in the form of work. This is an indicator of spontaneity of a reaction/physical change at constant pressure and temperature. The inputs are as follows:

• G is the change in Gibbs free energy
• H is the change in enthalpy
• T is temperature
• S is the change in entropy

G and H have units of joules (J), temperature is in Kelvin (K), and entropy has units of joules per Kelvin (J/K).

This equation is to be used with reactions that have changes in thermodynamic quantities.

See Also

UCDavis ChemWiki: Free Energy 

Wikipedia: Gibbs Free Energy

References

Whitten, et al. "Chemistry" 10th Edition. Pp. 592

[1] For the Spanish site click here