Change in standard Gibbs free energy

We calculate the change in standard Gibbs free energy using the AG° values for these aqueous ions in their standard states tabulated in Appendix D ... 

In biochemical literature, binding affinity is commonly expressed as the dissociation constant KV) (the reciprocal of the association constant KA), which can be expressed in terms of the equilibrium concentration of interacting species and from which the change in standard Gibbs free energy for binding (G ) may be calculated ... 

If the states before and after the reaction are kept standard and the change of entropy is (A5 ) (change of standard entropy), the change in standard Gibbs free energy (A5 ) is given by... 

If we know the standard Gibbs energies of formation of each substance for the original system AfG and the reaction system AfG, the change in standard Gibbs free energy AG is calculated by... 

The standard change in the Gibbs free energy AG for the reaction... 

The reversible work done per mol of electrons is the change in the Gibbs free energy, AG = tt eiec wS A. The standard cell potential is related to the standard free energy change by AG° = tt eiec = wS A °. 

If the change in the Gibbs free energy AG is greater than the changes in the enthalpy AH, the thermodynamic efficiency can exceed 1 (or 100%). Table 2 also lists the thermodynamic efficiencies for fuel cell reactions of interest under standard conditions. 

Now — RT In KP = AG° (Section 4.11), where AG° is the change in the Gibbs free energy for a mole of reaction with all reactants and products in their standard states at a pressure of 1 atm. 

It is known that the changes of standard Gibbs free energy and of enthalpy in the reaction are A( Se8=4000 cal mol and AH298= 19 000 cal mol. No data are available on heat capacities, but A and C are diatomic molecules, B is a linear triatomic molecule cuid is a non-linear triatomic molecule. 

Ideally, this reaction would take place at a potential of 1.229 V at standard conditions (25°C and 1 atm) if were it not for losses due to irreversible internal processes. In fact, the reversible potential Er of this reaction can be expressed in terms of the change in the Gibbs free energy, AG ... 

Exercise 6.8. Using values of " given in Table 6.2, determine the change in the Gibbs free energy under standard conditions for the redox reaction... 

The retention factor thus follows the rules of equilibrium thermodynamics, whereby the degree of retention is controlled by the change in the Gibbs free energy of the analyte molecule on going from the mobile into the stationary phase. This is in accordance with the general description of chemical equilibria in terms of standard free energies AG (Eq. 2) with universal gas constant R and absolute temperature T). 

Here AG = Ai/ — TA5 represents a standard change in the Gibbs free energy in the course of a realized chemical reaction. We have seen above that in the case of so-called ideal systems the equilibrium constant, coincides with the kinetically introduced equilibrium constant, and can easily be expressed as the ratio of the corresponding equilibrium concentrations of reagents to the power of their stoichiometric coefficients, i.e., as the left side of (2.4). In principle, this allows us to determine experimentally the equilibrium constant, by measuring the equilibrium concentrations of the reagents. 

The maximum electrical work in a fuel cell is obtained when all reactions are reversible with no losses and is equal to the change in the Gibbs free energy of formation at the reference standard temperature and pressure (STP), and it is given as... 

Having calculated the standai d values AyW and S" foi the participants in a chemical reaction, the obvious next step is to calculate the standard Gibbs free energy change of reaction A G and the equilibrium constant from... 

The standard Gibbs free energy change for a reaction refers to the process wherein the reaction proceeds isothermally, starting with stoichiometric quantities of reactants each in its standard state of unit activity and ending with products each at unit activity. In general it is nonzero and given by... 

As equation 2.4.8 indicates, the equilibrium constant for a reaction is determined by the temperature and the standard Gibbs free energy change (AG°) for the process. The latter quantity in turn depends on temperature, the definitions of the standard states of the various components, and the stoichiometric coefficients of these species. Consequently, in assigning a numerical value to an equilibrium constant, one must be careful to specify the three parameters mentioned above in order to give meaning to this value. Once one has thus specified the point of reference, this value may be used to calculate the equilibrium composition of the mixture in the manner described in Sections 2.6 to 2.9. 

Determine the change in the standard Gibbs free energy for the following reaction ... 

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