How is the free energy change, ΔG, calculated using ΔH and ΔS?

The free energy change, ΔG, is calculated using the relation ΔG = ΔH - TΔS, where ΔH represents the change in enthalpy, T is the absolute temperature in Kelvin, and ΔS is the change in entropy.

This formula illustrates how the spontaneity of a process is determined by both enthalpy and entropy contributions. The enthalpy term (ΔH) accounts for the heat absorbed or released during a reaction, while the entropy term (TΔS) represents the energy dispersal associated with the disorder within a system. When ΔH is positive (endothermic process) and ΔS is positive (increase in disorder), ΔG can be positive, indicating non-spontaneity at certain temperatures. Conversely, when ΔH is negative (exothermic process) and ΔS is also positive, ΔG will likely be negative, indicating spontaneity.

The correct relationship reflects how the change in free energy is influenced by both the energy content of the system (enthalpy) and the degree of disorder (entropy), with a temperature factor included to account for changes in thermal conditions. This combination is crucial in thermodynamics and allows for the prediction of whether a reaction will occur spontaneously under specific conditions.