A thermodynamic quantity that is a function of both the internal energy and entropy of a system, at equilibrium the free energy is at a minimum.
This is the energy that is actually available to do useful work. A decrease in free energy accompanies any spontaneous process.
Free Energy Change (ΔG)
The amount of free energy released (negative ΔG) or absorbed (positive ΔG) in a reaction at constant temperature and pressure.