Real free energies

Real Free Energy of Solvation of H+ and Absolute Potential of h( s) in Different Solvents ... 

Experimental determination of ATP, ADP, and Pj concentrations in brain, muscle, and liver, and a discussion of the problems in determining the real free-energy change for ATP synthesis in cells. 

Case, B. and Parsons, R. 1967, The real free energies of solvatation of ions in some non-aqueous and mixed solvents. Trans. Faraday Soc., 63,1224-1239. 

While AG j is the difference of the free energies of solvation of charged species i in two different solvent media, the direct transport of i from one solvent across the surfaces into the other solvent is described by the difference of real free energies of solvation, i.e., the real free energy of transfer Act which is directly measurable. 

Frumkin A. N. and Damaskin B. B. (1975), Real free energy of electron solvation during equilibrium of an electrode with a solntion , Dokl. Akad. Nauk. SSSR 221,395-398. 

An important aspect of this work is that it clearly defines the quantity being measured. The standard (real) free energy of solvation of an ion may be divided into a chemical term, and an electrical term, due to the electrical double layer at the surface i.e. 

Case and Parsons used the volta potential measurements directly to measure real free energies of transfer of an ion from water to a given solvent, i.e. 

From the observed xi and the extrapolated value of x, the standard real free energy of solvation is evaluated from... 

It is difficult to assess the origins of the discrepancies between these investigations since much of the data is based on values which differ considerably between the various authors. More recently, Takahashi found the difference in E between Rb and Tl to be 1.66 0.01 V in H2O-AN mixtures up to 40 mole per cent AN with the implication that this difference should hold in pure AN. Coetzee et find a value of 1.71 V for this difference in AN. In addition to these uncertainties, there is also the question of the validity of eqn. 2.7.3 which has no real advantage over the assumption that AC (Rb ) = 0.0. There also appears to be some confusion over the quantities actually required in order to relate e.m.f. s in one solvent to another. Parsons has, on several occasions, pointed out that the quantity required is the real free energy. A straight-forward application of the Born equation neglects the surface potential effect as well as other important ion-solvent and ion-ion interaction energies. 

An important concept for understanding the physical chemistry of a series of solvents involves relating the E value for a single electrode in one solvent to that in another. To accomplish this, we require knowledge of the real free energies of transfer of ions from one solvent to another. The Born equation (2.7.3) is unacceptable for this purpose. Even if this equation were valid, we would still be left with the problem of the x potential and the difference in the zFx energies between any two solvents (cf. eqn. 2.6.30). The Born equation has been the subject of critical examination and sect. 2.11. Table 2.7.20 demonstrates the failure of this relation as there is no correlation between AG° and the dielectric constant. For the transfer of ions from water to F(er = 109) and NMF( = 182), the Born equation requires that AG° is negative which is not observed (e.g. see Table 2.7.20). 

Using Randles results " for the real free energies of ions in water ( "af), Case and Parsons evaluated the corresponding quantities in... 

Measured Standard Molal Real Free Energies of Solvation of Ions in some Non-aqueous Solvents at 25 0 ... 

Hence the contribution to the measured real free energy of transfer by the surface potentials is about —7 kcal mol", which exceeds all the AGt(M ) values obtained by various procedures as shown in Appendix 2.11.7. 

J. E. B. Randles, Trans. Faraday Soc., 52, 1573 (1956) Randles work involves real free energies. 

B. Case and R. Parsons, Trans, Faraday Soc,y 63, 1224 (1967) these authors are reporting real free energies of transfer. 

We define the surface free energy Gg (J m" ) as the difference between the real free energy of the system, G, and the free energy that the system would have without surface effects, G ... 

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