Free Energy

Free energy is symbolized by the letter G. G can be defined as

G = H - TS

where H is enthalpy, T is the
temperature in Kelvin, and S is the entropy.

When a process is at a constant temperature,
then the change of free energy (can be given in the equation

G = H - TS

This equation cwill tell us that a process is spontaneous when free energy is negative(-G). When a process is at equilibrium, then G = 0.

S positve, H
negative |
Spontneous at all temperatures |

S positive, H
positive |
Spontaneous at high temperatures ( where exothermicity is relatively unimportant) |

S negative, H
negative |
Spontanous at low temperatures (where exothermicity is dominant) |

S negative, H
positive |
Process no
spontaeous at any tmperature (reverse process is
spontaneous at all temperatures) |