Reaction standard Helmholtz free energy

The molar standard-state free-energy change of a reaction (AG°) is a function of the equilibrium constant K) and is related to changes in the molar standard-state enthalpy (AH°) and entropy (A5°), as described by the Gibbs-Helmholtz equation ... 

The Van t Hoff isotherm establishes the relationship between the standard free energy change and the equilibrium constant. It is of interest to know how the equilibrium constant of a reaction varies with temperature. The Varft Hoff isochore allows one to calculate the effect of temperature on the equilibrium constant. It can be readily obtained by combining the Gibbs-Helmholtz equation with the Varft Hoffisotherm. The relationship that is obtained is... 

The present author has the impression from the literature on the stability of diazomethane relative to diazirine that two different physico-chemical phenomena were called (thermal) stability in some of the publications, namely the thermodynamic stability, as defined by the free energy of formation AGf and the free enthalpy of formation A//f for the (hypothetical) formation of a compound from the elements in a gas phase reaction under standardized conditions (298 K, 1 mol). AGf and A//f are related to one another by the free entropy A5f in the Gibbs-Helmholtz equation AGf = A/ff-TASf. The absolute values of AGf, A/ff and ASf do not give definite information on the stability of a compound, as this word is used in the everyday language of a chemist, because it is related to an unrealistic chemical process, namely the formation from the elements. If A/ff is known, however, for a given compound and for a real product of one of its reactions, the difference in magnitude of the two free enthalpies tells us whether this reaction is likely to take place, but we cannot depict at all, at least in principle, the half-life of such a reaction. 

The Gibbs-Helmholtz equation relates the standard free energy of reaction AG°, the standard enthalpy of reaction Ai/° and the standard entropy of reaction AS° ... 

Instead of measuring the equilibrium cell voltage Aeoo at standard conditions directly, this can be calculated from the reaction free energy AG for one formula conversion. In this context one of the fundamental equations is the GIBBS-HELMHOLTZ relation [7]. 

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