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In 1875, Josiah Gibbs proposed a thermodynamic quantity that combines enthalpy and entropy into a standard value, it was named Gibbs Free Energy.

ΔG=ΔG°+RTlnQ

Fin.

Gibbs Free Energy

SPONTANEOUS: G is negative (G< 0, Keq > 1)

NON-SPONTANEOUS: G is positive (G > 0, Keq < 1)

EQUILIBRIUM: G = 0 (Keq = 1)

Gibbs Free energy is a value based on the enthalpy and entropy of a reaction. It is the energy available to do work. It is most commonly used in the formula:

ΔG° = ΔH° - TΔS°

Review

It can also be used to calculate the K constant of a reaction using:

Application of Gibbs Free Energy in determining the spontaneity of a reaction

Gibbs free energy can be used as well in the Nernst equation to calculate standard cell potential

ΔG° = -nFE°

Endergonic - uses free energy, ΔG°>0

Exergonic - releases free energy, ΔG°<0

Endothermic - absorbs heat, ΔH°>0

Exothermic - releases heat, ΔH°<0

This can be used to determine spontaneity. Spontaneous reactions always have an excess of free energy

The most common formula using Gibbs free energy is:

ΔG°=ΔH°-TΔS°

It relates free energy to entropy and enthalpy

ΔG of formation

The Gibbs Free Energy of formation is the difference in free energy of the products minus reactants

The ΔG° of any free element in its standard state is zero

Gibbs Free Energy is defined as the energy associated with a chemical reaction that can be used to do work, its units are kJ/mol

Josiah Gibbs

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