Gibbs energy equilibrium and

Table 3-14. Gas phase Gibbs energies and equilibrium constants2...

This chapter contains a tabulation of Gibbs energies and equilibrium constants for various metabolic processes Involving phosphates. The temperature, pH, magnesium Ion concentration, and appropriate literature references are given. 

Gibbs energy and equilibrium constant of a chemical reaction depends on the local environment. For example, the equilibrium constant for protolytic reaction... 

A Note that any electrochemical cell, if left in a completed circuit, will eventually die as the redox reaction goes to completion. This means that the cell potential will eventually drop to zero. In Chapter 13, the relationship between Gibbs energy and equilibrium was established in a similar way. 

The chemical potential pi plays a vital role in both phase and chemical-reaction equilibria. However, the chemical potential exhibits certain unfortunate characteristics which discourage its use in the solution of practical problems. The Gibbs energy, and hence pi, is defined in relation to the internal energy and entropy, both primitive quantities for which absolute values are unknown. Moreover, pi approaches negative infinity when either P or Xi approaches zero. While these characteristics do not preclude the use of chemical potentials, the application of equilibrium criteria is facilitated by introduction of the fugacity, a quantity that takes the place of p. but which does not exhibit its less desirable characteristics. 

The units of AG are joules (or kilojoules), with a value that depends not only on E, but also on the amount n (in moles) of electrons transferred in the reaction. Thus, in reaction A, n = 2 mol. As in the discussion of the relation between Gibbs free energy and equilibrium constants (Section 9.3), we shall sometimes need to use this relation in its molar form, with n interpreted as a pure number (its value with the unit mol struck out). Then we write... 

Relation between standard reaction Gibbs free energy and equilibrium constant van t Hoff equation ... 

Let us assume the existence of a Taylor series for the Gibbs energy at the equilibrium point. This implies that the Gibbs energy and all its derivatives vary continuously at this point. The Taylor series is given as... 

Knowledge of these changes in standard Gibbs energy and enthalpy allows one to calculate the equilibrium composition and its variation with temperature. 

Example 3.15 Gibbs energy and distance from global equilibrium Discuss the effect of the distance from global equilibrium for a chemical reaction system R = P. 

Example 8.3 Temperature effect on equilibrium conversion Consider the elementary reversible reaction B P with no initial product P, while the initial concentration of B is B0. The standard Gibbs energy and standard enthalpy of the reaction are AG° (298.15K) = -14.1kJ/mol and A//" (298.15K) = -83.6kJ/mol. Assume that the specific heats of solutions are equal to that of water. Estimate the equilibrium conversion of B between 25°C and 120°C. 

When the pH is specified, the criterion for spontaneous change and equilibrium is provided by the transformed Gibbs energy and the reactants can be taken to be HgvM, HgvMOa, and O2 that are involved in the following biochemical reaction. 

In the system KCI-KBF4, for the Gibbs energy and of the equilibrium constant of the exchange reaction, the values ArGio43K = 302 kJ mol and Kkci = 10 , respectively, were calculated. Thus, for n > 10 , the degree of conversion is a = 0. Hence, the calculation confirms the experimental results that the exchange reaction in this system does not take place. 

The state variables T and p are particularly suited for systems at heterogeneous phase equilibrium because equilibrium phases coexist at uniform T and p. As the natural energy function of [T,p], the Gibbs energy and derived functions will be used to describe phase equilibrium. 

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