Gibbs function changes

In a similar way, we say that the value of the Gibbs function changes in response to changes in pressure and temperature. We write this as... 

The temperature dependence of the Gibbs function change is described quantitatively by the Gibbs-Helmholtz equation. 

Writing the equation in this way tells us that if we know the enthalpy of the system, we also know the temperature dependence of G -i-T. Separating the variables and defining Gj as the Gibbs function change at Ti and similarly as the value of G2 at T2, yields... 

As the two amalgams have the same solvent (mercury), we may choose the same standard state for Pb in each amalgam. We choose a Henry s-law standard state because we have data for dilute amalgams and the solubility of Pb in Hg is limited. Equation (16.18) then will represent the Gibbs function change for Equation (17.19) ... 

Now we can obtain the standard Gibbs function change for Equations (20.36), because the sum of Equations (20.37) through (20.39) yields... 

Having obtained the standard Gibbs function change accompanying the transfer of HCl from the gaseous to the aqueous state, we can add it to the standard Gibbs function for formation of gaseous HCl [11],... 

For the Gibbs function change in Equation (20.61), 02 of the undissociated species of succinic acid in the saturated solution is obtained as follows ... 

As in the case of Gibbs function changes, we also can divide the entropy change for a reaction [such as Equation (20.51)] into two parts and can assign one portion to each ion. As actual values of individual-ion entropies cannot be determined, we must establish some convention for apportioning the entropy among the constituent ions. 

With tables of ion entropies available, it is possible to estimate a Gibbs function change without the necessity of carrying out an experiment or seeking specific experimental data. For example, without seeking data for the potential of calcium electrodes, it is possible to calculate the calcium electrode potential or the Gibbs function change in the reaction... 

Reproducibility in the system was good, but various uncertainties limit the precision of the data. For instance, the solid phase probably contained both a and p UH3. The enthalpy difference between these species is unknown, and the heat capacity data for UH3 does not extend to the relevant temperature range (316a). Recent analyses of all the data suggest best values of -126.99 and -72.61 kJ moF for the standard enthalpy and Gibbs function changes on formation at 298 K and an S° value of 63.67 J mol 1 for UH3 (3d, 316b). 

It is AG, the standard molar Gibbs function change, that is directly related to the equilibrium constant. The two terms are related via the equation... 

In order to make calculations from this equation, two of the terms are combined to give a Gibbs function change for the reaction, AG, which is still standard in terms of mole fractions, but which applies to the particular SCF conditions used, where... 

There are two main physical reasons, which define intercommunication of fractal essence and local order for solid-phase pol miers the thermodynamical nonequilibrium and dimensional periodicity of their structure. In Ref. [9], the simple relationship was obtained between thermod5mamical nonequilibrium characteristic - Gibbs function change at self-assembly (cluster structure formation of pol miers AG - and clusters relative fraction (p jin the form ... 

We must not confuse the free enthalpy change AGsyst accompanying a chemical reaction and the molar reaction Gibbs function change ArG. They do not have the same mathematical status. The former change is a difference, the latter a partial... 

The terms enclosed within parentheses in Eqs. (2.10) and (2.11) are respectively called the standard molar reaction Gibbs function change A,G and the standard chemical affinity A°. By setting up... 

In order to determine the standard molar reaction Gibbs function change ArG°, the standard states of the reaction reactants and products must be defined. They must be chosen or, at a minimum, they must correspond to physical states, such as the physical property differences between them being endowed with an unambiguous physical meaning. As an example, a possible standard state of a solute is the state in which its concentration is 1 mol/L and in which the solution it forms with the solvent is an ideal one. Standard states are chosen conventionally for practical reasons. Fortunately, the conventions are universally agreed upon. 

The fact that standard states are conventional may be somewhat troublesome. Indeed, the question immediately arises about equilibrium constant values with different arbitrarily chosen standard states. Quite evidently, when standard states other than the usual ones are chosen, the value of the standard molar reaction Gibbs function change ArG° is different according to Eq. (2.14), it is also the case with K°. However, this is not the case with A G and AGgyst, which remain constant for a given process regardless of the adopted conventions. Actually, in Eq. (2.12),... 

We must emphasize two points. The first one has already been mentioned. The molar reaction Gibbs function change is endowed with an instantaneous value. It depends on the reaction extent and, of course, on the initial reactants and products concentrations. As a result, the potential difference E is also instantaneous. This is the reason why the above reasoning involved differential quantities. 

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