Gibbs Free Energy and Thermodynamic Favorability

The concept of Gibbs Free Energy (G) arises from the second and third laws of thermodynamics.
It represents the maximum reversible work a thermodynamic system can do at constant temperature and pressure.
The Gibbs energy change (ΔG) determines the spontaneity of a chemical process.
A negative ΔG denotes a spontaneous reaction, while a positive ΔG signifies a non-spontaneous one.
A reaction with ΔG equals zero is in a state called dynamic equilibrium.

Thermodynamic Favorability refers to the likelihood of a reaction under particular conditions, primarily dictated by changes in enthalpy (ΔH) and entropy (ΔS).
The principle comes from the equation, ΔG = ΔH - TΔS, indicating that Gibbs free energy depends on the enthalpy, temperature, and entropy.
Processes with a large negative enthalpy (ΔH) change or a large positive entropy (ΔS) change are likely to occur spontaneously as they lead to a decrease in ΔG.
However, reactions with unfavorable ΔH and ΔS values can occur under different temperature conditions as ‘T’ influences the spontaneity of a reaction.

Gibbs Free Energy has various applications in chemical and biochemical systems.
It helps predict the direction of chemical reactions and biochemical pathways.
In electrochemistry, it is applied to establish the potential of electrochemical cells, give substance to the Nernst equation and predict the potential of half-reactions.
Industries like petroleum refining, food science, and pharmaceuticals apply the principles of Gibbs free energy to guide the development of new products and improve existing processes.
In environmental chemistry, it aids in predicting the behaviour and fate of chemical pollutants.

Phase transitions like melting, freezing, vaporization, condensation etc., are also influenced by Gibbs free energy.
The phase that has the lowest Gibbs free energy under given conditions will form preferentially.
Thus, understanding Gibbs free energy aids in predicting the phase of matter under various conditions.