Isothermal processes Gibbs free energy

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... 

The Gibbs free energy change during a reaction is a measure of the reversible work (other than pressure-volume work) that can be obtained from the process at constant T and p. Since cellular processes are isothermal and isobaric, free energies are the quantities of choice in studying metabolic processes with respect to their ability to carry out the work of cells. 

Here, the A operator describes the change in the associated parameter from outlet to inlet. The first term on the right hand side (which is the change in Gibbs free energy due to isothermal electrochemical reaction) describes the maximum theoretical work that is possible from the process. If we subtract from this the actual work, /gen. we have the internal heat generation due to all internal loss mechanisms ... 

It emerges from thermodynamics that the overall thermodynamic criterion for spontaneity is vested in a quantity defined as the Gibbs (free) energy change, AG which, for an isothermal (Frame 1) process, is defined by the equation ... 

Any biochemical reaction that occurs spontaneously or that emits a net amount of energy will have a negative free energy value. In this form, chemical potential and Gibbs free energy can be used interchangeably for isothermal (constant T) and isobaric (constant p) chemical processes. 

Generally, for equilibrium processes dG = 0. For nonequilibrium states and irreversible processes we have dGisothermal-isobaric conditions, any dissipation of Gibbs free energy... 

For a fixed volume, isothermal and reversible process, the differential of the Gibbs free energy is given by ... 

In CPA-rich blends, both the enthalpy and entropy of mixing are positive and, as a result, the Gibbs free energy of mixing (which is the difference between a relatively large enthalpy term and a smaller entropy term) would also become positive. The process may be similar to the isothermal fusion of CPA crystallites present in its structure under the influence of chitosan, which acts as a macromolecular solvent in the blend. The need for CPA fusion is an obstacle to its compatibility with chitosan, and the blends would tend to phase-separate, at least potentially. 

The maximum work obtainable from an isothermal continuous process is the negative of the Gibbs free energy change between the product and reactant streams -yG When an oxidation reaction, e.g.. 

The energy change for any equimolar process occurring at constant temperature is a work process. If the isothermal, equimolar process is carried out reversibly at constant pressure, the work is Gibbs free energy. If the isothermal process is carried out reversibly at constant volume, the work is Helmholtz free energy. 

It is also seen that the exergy change is equal to the change in Gibbs free energy when the process is carried out isothermally at T. ... 

All of the previous equations were valid at atmospheric pressure. However, a fuel cell may operate at any pressure, typically from atmospheric all the way up to 6-7 bar. For an isothermal process, and with a little bit of basic thermodynamics [4], the change in Gibbs free energy may be shown to be ... 

---