A negative change in this quantity characterizes a spontaneous process.
This quantity's derivative with respect to particle number is the chemical potential. The equilibrium constant of a chemical reaction can be expressed as the exponential of the change in this quantity over the temperature. This quantity measures the useful work obtainable from a system at constant pressure, and this quantity may be calculated by subtracting the product of temperature and entropy from the enthalpy. A negative change in this quantity characterizes a spontaneous process. For 10 points, name this type of free energy named for an American and contrasted with Helmholtz.
This quantity's derivative with respect to particle number is the chemical potential.
{Gibbs Free Energy} [prompt on partial answer, accept "Gibbs" at the end, prompt on "G"]