Helmholtz Free Energy
Energy released or absorbed in a reaction occurring reversibly at constant volume and temperature.
Can be used to predict whether a process will occur spontaneously at constant volume and temperature.
A = Helmholtz Free Energy [J]
U = Internal Energy [J]
T = Temperature [K]
S = Entropy [JK-1]
Changes in Helmholtz Free Energy correspond to changes in free energy for processes occuring at constant temperature and volume. The sign of δA is negative for spontaneous processes and zero for processes at equilibrium.