What is the role of Gibbs free energy in determining reaction spontaneity?

Gibbs free energy determines reaction spontaneity by measuring the energy available to do work.

Gibbs free energy (ΔG) is a thermodynamic property that measures the energy available to do work in a system. It takes into account both the enthalpy (ΔH) and entropy (ΔS) changes of a reaction. A negative ΔG indicates that the reaction is spontaneous and can occur without the input of external energy. A positive ΔG indicates that the reaction is non-spontaneous and requires the input of external energy to occur.

The relationship between ΔG and spontaneity can be explained by the second law of thermodynamics, which states that in any spontaneous process, the entropy of the universe increases. A spontaneous reaction has a negative ΔG because it releases energy, increasing the entropy of the system and the surroundings. In contrast, a non-spontaneous reaction has a positive ΔG because it requires energy input, decreasing the entropy of the system and the surroundings.

The magnitude of ΔG also determines the extent to which a reaction will proceed towards completion. A large negative ΔG indicates that the reaction is highly exergonic and will proceed to completion, while a small negative ΔG indicates that the reaction is only slightly exergonic and will reach equilibrium. A positive ΔG indicates that the reaction is endergonic and will not proceed spontaneously.

In summary, Gibbs free energy is a crucial factor in determining reaction spontaneity and the extent to which a reaction will proceed towards completion. Understanding the relationship between ΔG and spontaneity is essential for predicting and controlling chemical reactions.