114 Gibbs free energy
Gibbs free energyis represented by the following equation:
∆G =∆H -T∆S
∆G is the change in Gibbs free energy.
∆H is the change in potential energy, sometimes known as the enthalpy of a system.
T is the temperature in Kelvin.
∆S is a statistical correlation, known as the entropy of a system.The basic principle is that totalentropy increases. This increase can be because of an
increase in the entropy of the chemicals,∆S, or because the reaction has produced heat,
increasing the entropy of the environment.
The Gibbs free energy lets us calculate the total increase in entropy, including the effects
on the environment, without needing to know anything about the environment.
Atlowtemperatures,∆Gis approximately∆H, and nature favours the reaction with lowest
energy products, which release the most heat. This mayreducethe entropy of thesystem,
but theincreasein the entropy of theenvironmentmore than compensates.
Athightemperatures,∆Gis approximately-T∆S, and nature favours the reaction with
high energy products, which may actually absorb heat. This mayreducethe entropy of the
environment, but theincreasein the entropy of thesystemmore than compensates.
Either way, the Gibbs free energyalwaysdecreases.