Enthalpy, entropy and free energy

A general prerequisite for the existence of a stable interface between two phases is that the free energy of formation of the interface be positive were it negative or zero, fluctuations would lead to complete dispersion of one phase in another. As implied, thermodynamics constitutes an important discipline within the general subject. It is one in which surface area joins the usual extensive quantities of mass and volume and in which surface tension and surface composition join the usual intensive quantities of pressure, temperature, and bulk composition. The thermodynamic functions of free energy, enthalpy and entropy can be defined for an interface as well as for a bulk portion of matter. Chapters II and ni are based on a rich history of thermodynamic studies of the liquid interface. The phase behavior of liquid films enters in Chapter IV, and the electrical potential and charge are added as thermodynamic variables in Chapter V. 

In a parallel study Goursot and Wadso (322) determined calorimetri-cally the free energies, enthalpies, and entropies of dissociation of the conjugate acids of thiazoles in aqueous media (Table 1-51). 

Alberty, R. A., 1969. Standard Gibb.s free energy, enthalpy, and entropy change.s a.s a function of pH and pMg for reaction.s involving adeno.sine pho.sphate.s. of Biological Chemistry 244 3290-3302. 

Tautomerism of 2-substituted hexahydropyrimidines has been studied (980PP53), and free energies, enthalpies, and entropies of activation for this ring-chain tautomeric equilibrium have been measured [97JCS(P2)169]. 

Standard Free Energies, Enthalpies, and Entropies of Formation of Palladium and Nickel Hydrides ... 

The standard free energies, enthalpies, and entropies calculated from the experimental data for the reaction 4Me + Hj = 2Me2H (where Me = Pd or Ni), at 1 atm of hydrogen pressure and 298°K. 

The net retention volume and the specific retention volume, defined in Table 1.1, are important parameters for determining physicochemical constants from gas chromatographic data [9,10,32]. The free energy, enthalpy, and. entropy of nixing or solution, and the infinite dilution solute activity coefficients can be determined from retention measurements. Measurements are usually made at infinite dilution (Henry s law region) in which the value of the activity coefficient (also the gas-liquid partition coefficient) can be assumed to have a constant value. At infinite dilution the solute molecules are not sufficiently close to exert any mutual attractions, and the environment of each may be considered to consist entirely of solvent molecules. The activity... 

When retention ordering can be established, the theoretical peak capacity could be effectively utilized in a multidimensional separation system in a far more efficient manner. However, one is reminded that with the exception of synthetic polymers and a few other special cases of small molecules, real samples have almost random retention time distributions. It is rare when the free energy, enthalpy, and entropy of interaction are determined in LC for molecules utilized in retention mechanism studies. However, the retention energetics have been determined in GC studies by Davis et al. (2000) who found that many complex samples will exhibit Poisson distributions of retention times due to a Poisson distribution in enthalpy and a compensating distribution in entropy. 

It is well known that such quantities as the standard free energy, enthalpy and entropy display a remarkable tendency to be additive functions of independent contributions of part-structures of the molecule. This property, on which the mathematical simplicity of many extrathermodynamic relationships is largely based, is well illustrated, for example, by the enthalpies of formation at 298°K of several homologous series of gaseous hydrocarbons Y(CH2)mH, which are expressed by the relation (28) (Stull et al., 1969). In... 

After this computer experiment, a great number of papers followed. Some of them attempted to simulate with the ab-initio data the properties of the ion in solution at room temperature [76,77], others [78] attempted to determine, via Monte Carlo simulations, the free energy, enthalpy and entropy for the reaction (24). The discrepancy between experimental and simulated data was rationalized in terms of the inadequacy of a two-body potential to represent correctly the n-body system. In addition, the radial distribution function for the Li+(H20)6 cluster showed [78] only one maximum, pointing out that the six water molecules are in the first hydration shell of the ion. The Monte Carlo simulation [77] for the system Li+(H20)2oo predicted five water molecules in the first hydration shell. A subsequent MD simulation [79] of a system composed of one Li+ ion and 343 water molecules at T=298 K, with periodic boundary conditions, yielded... 

In the formation of activated complex, if AG, AH and AS are change in free energy, enthalpy and entropy, respectively, for one gram mole of the substance, then equilibrium constant... 

These parameters (AG, A//, and A5 ) differ slightly from normal standard parameters in that the contribution of motion along the reaction coordinate toward the transition state is not included. The values are the difference in free energy, enthalpy, and entropy between 1 mole of activated complex and 1 mole of each reactant, all substances being at their standard-state concentrations (usually 1 M). 

Which is the correct formulation for the relationship between free energy, enthalpy and entropy ... 

Tab. 8.1 Standard free energies, enthalpies and entropies of formation of the iron oxides at 0.1 MPa and 298 K...

Tab. 8.2 Standard free energies, enthalpies and entropies for soluble Fe and some other species (25 °C)...

The results of the salt effect studies undertaken by Aveyard and Heselden (49) agree with those obtained by the present authors. Aveyard and Heselden measured the changes in free energy, enthalpy, and entropy associated with the... 

Table IV. Standard Free Energy, Enthalpy, and Entropy of Transfer of n-Bu4NBr from Water to Water—Acetone Mixtures at 298.15°K...

Table 33 Excess Free Energies, Enthalpies, and Entropies of Hexane (apolar), Benzene (monopolar), Diethylether (monopolar), and Ethanol (bipolar) in the Ideal Gas Phase, in Hexadecane, and in Water at Infinite Dilution.0 All Data at 25°C. Reference Pure Liquid Organic Compound.

Table 3.4 Air-Hexadecane, Air-Water, and Hexadecane-Water Equilibrium Partitioning of Hexane, Benzene, Diethylether, and Ethanol Free Energies, Enthalpies, and Entropies of Transfer, as well as Partition Constants Expressed on a Molar Base (i.e., mol U phase 1/mol L/ phase 2)...

Under the conditions existing in biological systems (including constant temperature and pressure), changes in free energy, enthalpy, and entropy are related to each other quantitatively by the equation... 

Denison, J. T., and J. B. Ramsey The free energy, enthalpy and entropy of dissociation of some perchlorates in ethylene chloride and ethylidene chloride. J. Am. Chem. Soc. 77, 2615 (1955). 

The determination of the adsorption parameter (Vg) at three temperatures permits the calculation of the free energy, enthalpy, and entropy of adsorption. A plot of log Vg versus 1/T has a slope of -AHa(js/2.3R. AGacjs is obtained by... 

Free energies, enthalpies, and entropies of ionization for a number of reducing sugars have been determined by Christensen and co-workers (13). Their data, however, are for equilibrium mixtures of anomers rather than for individual anomeric forms. 

It has been pointed out6 that trans-1,4-dihalocyclohexanes are ideally suited for determination of changes in free energy, enthalpy, and entropy by electron diffraction, since the ratio between the conformers may be found quite accurately by comparing areas of the appropriate peaks in the experimental RD curve (see Fig. 17). Accurate thermodynamic parameters of gas phase conformational equilibria are rather scarce and these molecules may perhaps be able to provide some much-wanted high-quality data with the aid of the modern electron-diffraction technique. 

Free energy, enthalpy and entropy of immersion are related by... 

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