One may derive this by utilizing the Legendre transform on the internal energy of a system.
The Clausius-Clapeyron equation assumes the change in this to be zero. Because this quantity is most useful when the substance in question is both isothermal and isobaric, a different quantity is used for explosive substances. An equation partially due to the namesake of this quantity gives the temperature dependence of this quantity for an ideal gas. A zero change in this quantity for a system implies that the system is in equilibrium, but a negative value for this quantity implies that a reaction is spontaneous. One may derive this by utilizing the Legendre transform on the internal energy of a system. For ten points, name this state function named for its American inventor, which measures the maximum amount of work attainable from a system, defined as enthalpy minus the product of temperature and entropy.
The Clausius-Clapeyron equation assumes the change in this to be zero.
Gibbs Free Energy