Electrochemical free energy change

Electrochemical equilibrium is established at each interface of the cell when the -> electrochemical potentials of the common components of the two phases (a and f) forming the interface are equal, that is pf = ji , and the electrochemical free energy change (AG) for the process occurring at the interface is zero. For the net cell reaction given above, such considerations lead to an expression for the electrochemical equilibrium constant Ka given by [i]... 

Note that (2.3.19) and (2.3.20) are at strict equilibrium under the null-current condition hence the electrochemical free energy change for each of them individually is zero. Of course, this is also true for their sum ... 

Let us focus first on the net chemical reaction, (2.3.22). Since the electrochemical free energy change is zero,... 

The electrochemical free energy change at equihbrium and reduction is depicted in Fig. 3.1. As shown in Fig. 3.1a, the difference between the cathodic and anodic activation... 

Fig. 3.1 Electrochemical free energy change (a) at equilibrium and (b) when the oxidized species are reduced.

Before we will discuss the electrochemical system, it is important to define the properties and characteristics of each component, especially the electrolyte. In the following, we assume macroscopic amounts of an electrolyte containing various ionic and nonionic components, which might be solvated. In the case that this bulk electrolyte is in thermodynamic equilibrium, each of the species present is characterized by its electrochemical potential, which is defined as the free energy change with respect to the particle number of species i ... 

Before dealing with various important applications of the electrochemical series with some practical examples, a break is given here to present a more detailed elaboration on the hydrogen electrode, reference electrodes, and some of the theoretical and general aspects pertaining to electrode potentials and free energy changes involved with cell reactions. 

If the combination of oxygen and carbon at the anode is included in the electrochemical reaction then the free energy change is much smaller. For the reaction... 

Figure 6.1. Free-energy change for the general electrochemical reaction, Eq. (6.6) initial state, Ox, in the bulk of the solution, outside the diffusion double layer final state. Red, in the bulk of the solution outside the diffuse double layer.

The thermodynamic criterion for spontaneity (feasibility) of a chemical and electrochemical reaction is that the change in free energy, AG have a negative value. Free-energy change in an oxidation-reduction reaction can be calculated from knowledge of the cell voltage ... 

A fuel cell is a device that converts the free energy change of a chemical reaction directly into electrical energy. This conversion occurs by two electrochemical half cell reactions. 

Biochemical reactions are basically the same as other chemical organic reactions with their thermodynamic and mechanistic characteristics, but they have the enzyme stage. Laws of thermodynamics, standard energy status and standard free energy change, reduction-oxidation (redox) and electrochemical potential equations are applicable to these reactions. Enzymes catalyse reactions and induce them to be much faster . Enzymes are classified by international... 

Equation (5) shows the fundamental relationship between Gibbs free energy change of the chemical reaction and the cell potential under reversible conditions (potential of the electrochemical cell reaction). 

As we showed in Chapter 11, the free-energy change for the creation of an electrochemical gradient by an ion pump is... 

Thus, the electron flows from the reductant to the oxidant through photoexcited semiconductor particles. Therefore, the particle suspended in a solution of reductant and oxidant can be regarded as a very small electrochemical cell in which the irradiated light energy is used as free energy change and/or activation energy of the redox reaction of the reductant and the oxidant (Fig. 11.2). 

We ve now seen two quantitative measures of the driving force of a chemical reaction the cell potential E (an electrochemical quantity) and the free-energy change AG (a thermochemical quantity, Section 17.7). The values of AG and E are directly proportional and are related by the equation... 

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