The equation for Gibbs Free Energy (that is, the equation that DEFINES Gibbs Free Energy in the form of an equation) is G = U + pV – TS,

where G is Gibbs Free Energy, U is the internal energy (this unit is measured in Joules), p is the pressure exerted (this is measured in pascals), V is the volume observed (measured in cubic meters), T is the temperature of the system (measured in Kelvin), and S is the entropy (measured in Joules per Kelvin). Another equation for Gibbs Free Energy would be G = H – TS, in which H is enthalpy (measured in Joules).

Either way, the result of these equations are essentially the same – you would come up with the value of the Gibbs Free Energy in that context. It should be interesting to note that H and S in this context presume that the values were found at Standard Temperature and Pressure – meaning a closed system.

The equations for Gibbs Free Energy change drastically in an open system, because there are of course different external factors that affect the resulting amount of Gibbs Free Energy.

In this section of the site, we will further show you how the equation for Free Gibbs Energy works, and how to calculate for Free Gibbs Energy in an open system.