How do enthalpy and entropy changes interplay in determining Gibbs free energy?

Gibbs free energy is determined by the interplay of enthalpy and entropy changes in a system.

The Gibbs free energy change (ΔG) in a system is a measure of the maximum reversible work that a system can perform at constant temperature and pressure. It is calculated using the equation ΔG = ΔH - TΔS, where ΔH is the change in enthalpy, T is the absolute temperature and ΔS is the change in entropy.

Enthalpy (H) is a measure of the total energy of a system. It includes the internal energy of the system (the energy required to create the system in the first place) and the energy required to make room for the system by displacing its environment. A negative change in enthalpy (ΔH) corresponds to an exothermic reaction, where heat is released, while a positive ΔH corresponds to an endothermic reaction, where heat is absorbed.

Entropy (S), on the other hand, is a measure of the disorder or randomness of a system. An increase in entropy (positive ΔS) corresponds to an increase in disorder, while a decrease in entropy (negative ΔS) corresponds to a decrease in disorder.

The interplay between these two factors determines the Gibbs free energy change and thus the spontaneity of a reaction. If ΔG is negative, the reaction is spontaneous; if ΔG is positive, the reaction is non-spontaneous; and if ΔG is zero, the system is in equilibrium.

For example, in an exothermic reaction (negative ΔH) that also increases the disorder of the system (positive ΔS), the Gibbs free energy change will be negative, indicating a spontaneous reaction. However, if the reaction is endothermic (positive ΔH) and decreases the disorder of the system (negative ΔS), the Gibbs free energy change will be positive, indicating a non-spontaneous reaction.

In summary, the interplay between enthalpy and entropy changes is crucial in determining the Gibbs free energy change and thus the spontaneity of a reaction. Understanding this interplay is key to predicting the behaviour of chemical systems.