Gibbs free energy

Gibbs Free Energy (G), named after Josiah Willard Gibbs, is a thermodynamic quantity that measures the maximum amount of reversible work that can be performed by a thermodynamic system at a constant temperature and pressure. It is a central concept in the fields of Chemistry and Physics, particularly within the study of Thermodynamics and Physical Chemistry. The Gibbs free energy is a potential that predicts the direction of chemical reactions and phase changes.

Definition

The Gibbs free energy, G, is defined as:

G = H - TS

where:

• H is the Enthalpy of the system,
• T is the Temperature in Kelvin,
• S is the Entropy of the system.

The change in Gibbs free energy, ΔG, during a process is given by:

ΔG = ΔH - TΔS

where Δ signifies the change in the respective quantities. A negative ΔG indicates that a process is spontaneous, while a positive ΔG suggests that it is non-spontaneous under constant temperature and pressure.

Applications

Gibbs free energy has wide applications in both chemistry and physics. It is used to predict the spontaneity of reactions, determine the equilibrium position of chemical reactions, and understand phase changes. In Electrochemistry, the Gibbs free energy is related to the electromotive force of a galvanic cell and is crucial in designing batteries and fuel cells.

Gibbs Free Energy and Equilibrium

The condition for equilibrium in a chemical reaction is ΔG = 0. At equilibrium, the system's Gibbs free energy is at its minimum value, and there is no net change in the composition of the system. This principle is used to derive the Equilibrium Constant for chemical reactions.

Temperature Dependence

The sign and magnitude of ΔG depend on the temperature, as seen from the equation ΔG = ΔH - TΔS. This temperature dependence is crucial in processes like Protein Folding, where the balance between enthalpy and entropy determines the structure and stability of proteins.

Relation to Other Thermodynamic Quantities

Gibbs free energy is closely related to other thermodynamic quantities such as the Helmholtz Free Energy, which is used under conditions of constant volume. The relationship between Gibbs free energy and the Partition Function is fundamental in Statistical Mechanics, linking thermodynamics with microscopic properties of systems.

Conclusion

Understanding Gibbs free energy is essential for predicting the direction and extent of chemical reactions, designing energy-efficient systems, and exploring the fundamental principles of thermodynamics. Its application spans across various scientific disciplines, making it a cornerstone concept in the study of physical sciences.

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  Gibbs free energy diagram

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  Gibbs-Helmholtz equation

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  Thermodynamics Gibbs E0 Ecell pH

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  Gibbs-Maxwell surfaces