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In thermodynamics, the Gibbs free energy (or Gibbs energy as the recommended name; symbol ) is a thermodynamic potential that can be used to calculate the maximum amount of work, other than pressure–volume work, that may be performed by a thermodynamically closed system at constant temperature and pressure.
The standard Gibbs free energy of formation (G f °) of a compound is the change of Gibbs free energy that accompanies the formation of 1 mole of a substance in its standard state from its constituent elements in their standard states (the most stable form of the element at 1 bar of pressure and the specified temperature, usually 298.15 K or 25 °C).
The green curve is the total (Gibbs if this is at constant pressure) free energy as a function of radius. Shown is the free energy barrier, , and radius at the top of the barrier, . This total free energy is a sum of two terms. The first is a bulk term, which is plotted in red.
For a similar process at constant temperature and volume, the change in Helmholtz free energy must be negative, <. Thus, a negative value of the change in free energy (G or A) is a necessary condition for a process to be spontaneous. This is the most useful form of the second law of thermodynamics in chemistry, where free-energy changes can be ...
Several free energy functions may be formulated based on system criteria. Free energy functions are Legendre transforms of the internal energy. The Gibbs free energy is given by G = H − TS, where H is the enthalpy, T is the absolute temperature, and S is the entropy. H = U + pV, where U is the internal energy, p is the pressure, and V is the ...
It describes how the Gibbs free energy, which was presented originally by Josiah Willard Gibbs, varies with temperature. [1] It was derived by Helmholtz first, and Gibbs derived it only 6 years later. [2] The attribution to Gibbs goes back to Wilhelm Ostwald, who first translated Gibbs' monograph into German and promoted it in Europe. [3] [4]
Two methods to extract the Gibbs free energy based on the value of CMC and exist; Phillips method [3] based on the law of mass action and the pseudo-phase separation model. The law of mass action postulates that the micelle formation can be modeled as a chemical equilibrium process between the micelles M n {\displaystyle M_{n}} and its ...
More specifically, we can write the Gibbs free energy of activation in terms of enthalpy and entropy of activation: ΔG ‡ = ΔH ‡ − T ΔS ‡. Then, for a unimolecular, one-step reaction, the approximate relationships E a = Δ H ‡ + RT and A = ( k B T / h ) exp(1 + Δ S ‡ / R ) hold.