Gibbs energy electricity

Gibbs energy for the adsorption of water and the interfacial parameter, 187 Gokstein and the piezo electric method for the determination of the potential of zero charge, 42 Gold... 

During ATP synthesis, protons move down these gradients from outside [Hour] into the mitochondrial matrix each proton doing both electrical and osmotic work (due to the concentration difference) so that the Gibbs energy change is... 

One main advantage of such a power source is the direct transformation of the chemical energy of methanol combustion into electrical energy. Hence, the reversible cell potential, can be calculated from the Gibbs energy change, AG, associated with the overall combustion reaction of methanol (1), by the equation ... 

This equation links the EMF of a galvanic cell to the Gibbs energy change of the overall current-producing reaction. It is one of the most important equations in the thermodynamics of electrochemical systems. It follows directly from the first law of thermodynamics, since nF% is the maximum value of useful (electrical) work of the system in which the reaction considered takes place. According to the basic laws of thermodynamics, this work is equal to -AG . 

The open cell discussed was considered as an equilibrium cell since equilibrium was established across each individual interface. However, the cell as a whole is not in equilibrium the overall Gibbs energy of the full reaction is not zero, and when the circuit is closed, an electric current flows that is attended by chemical changes (i.e., a spontaneous process sets in). 

First, electric work wx and w2 is calculated for a single ion species denoted as k. For wx the same procedure as for the quantity w2 in the Born treatment of solvation Gibbs energy (Eq. (1.2.5) will be used giving (e = De0))... 

When the adsorbed components are electrically charged, then the partial molar Gibbs energy of the charged component depends on the charge of the given phase, and thus the chemical potentials in the above relationships must be replaced by the electrochemical potentials. The Gibbs adsorption isotherm then has the form... 

As depicted in Fig. 5, both the protein molecule and the sorbent surface are electrically charged. In an aqueous environment, they are surrounded by counterions, which, together with the surface charge, form the so-called electrical double layer. The Gibbs energy of an electrical double layer, may be calculated as the isothermal, isobaric reversible work required to invoke the charge distribution in the double layer... 

An electrical potential difference between the electrodes of an electrochemical cell (called the cell potential) causes a flow of electrons in the circuit that connects those electrodes and therefore produces electrical work. If the cell operates under reversible conditions and at constant composition, the work produced reaches a maximum value and, at constant temperature and pressure, can be identified with the Gibbs energy change of the net chemical process that occurs at the electrodes [180,316]. This is only achieved when the cell potential is balanced by the potential of an external source, so that the net current is zero. The value of this potential is known as the zero-current cell potential or the electromotive force (emf) of the cell, and it is represented by E. The relationship between E and the reaction Gibbs energy is given by... 

The determination of the Gibbs energy of adsorption at zero surface coverage AGg=o nd of the interaction parameter A as a function of an electrical variable, may become a valuable source of information on the interactions at the interface. The value of AG°can be considered as the energy required to replace n monomolecularly adsorbed solvent molecules from a fully solvent-covered electrode surface by one monomeric molecule of the solute... 

As mentioned earlier, the Gibbs energy of adsorption can be analyzed using one of two independent electrical variables potential or charge density. The problem was discussed by Parsons and others, but it was not unequivocally solved because both variables are interconnected. Recent studies of the phase transition occurring at charged interfaces, performed at a controlled potential, show that if the potential is... 

The AG° values of acetone adsorption decrease slightly in the sequence H2O,Me0H, NM. They are indicative of a weak physical adsorption at the Hg/solution interface. It is also evident that the Gibbs energy of adsorption is enhanced by the electric field, particularly at the point of adsorption maximum. Small values of AG , similar to those determined at the solution/air interface, attest to the absence of specific interactions cf acetone with the mercury surface (which is opposite to the TU adsorption case). Hence, the solute-solvent interaction in the solution is an important factor in the adsorption of acetone, as shown for the zero charge on the Hg electrode in Fig. 11. 

The consumed electrical energy is 17 7 (U, cell voltage [V], 7, cell current [A]). The part U I — AH, that exceeds the enthalpy of the cell reaction AH = AG + T AS (AG, reaction free enthalpy (Gibbs energy)... 

One may also look at the effect of the electrodes from the point of view of energy balance. Measurement of voltages always requires at least a small electrical current. This corresponds in the case of galvanic cells to the transfer of electroactive species from one electrode to the other. The corresponding chemical work is the change of the Gibbs energy, AG, which... 

This Gibbs energy of reaction is converted into the electrical energy zq dSE. Then we have for the cell voltage... 

Standard Gibbs energy of the ion transfer Electric current, A... 

A particular component of a given phase can be characterized in terms of its content and ability to partake in various processes (chemical reactions, transport processes) using the partial molar Gibbs energy. For an electrically-charged phase, this quantity is termed the electrochemical potential of the ith component... 

The DEFC transforms directly the Gibbs energy of combustion of ethanol into electricity, without a fuel processor. This greatly simplifies the system, reducing its volume and cost [22, 23]. The important development of DEFCs is due to the use of a proton exchange membrane as electrolyte, instead of a liquid add electrolyte, as done previously. 

For an electrically neutral molecule, the solvation energy AG"V is equal to the Gibbs energy of transfer, AG/, of the molecule from a vacuum into the solvent. However, for an electrically charged ion, the following relationship holds ... 

An equilibrium electrical potential is associated with a Gibbs energy of formation by the equation... 

In heterogeneous solid state reactions, the phase boundaries move under the action of chemical (electrochemical) potential gradients. If the Gibbs energy of reaction is dissipated mainly at the interface, the reaction is named an interface controlled chemical reaction. Sometimes a thermodynamic pressure (AG/AK) is invoked to formalize the movement of the phase boundaries during heterogeneous reactions. This force, however, is a virtual thermodynamic force and must not be confused with mechanical (electrical) forces. 

Often, however, it is more realistic to abandon the model of a discontinuous interface. Segregation of impurities and other point defects, as well as elastic and electric fields, broaden the interface region. For this extended boundary, we can formulate j the Gibbs energy of Eqn. (10.1) as (< = A,B) j... 

In a foregoing section, we mentioned that field forces (e,g., of the electric or elastic field) can cause an interface to move. If they are large enough so that inherent counterforces (such as interface tension or friction) do not bring the boundary to a stop, the interface motion would continue and eventually become uniform. In this section, however, we are primarily concerned with boundary motions caused by chemical potential changes. From irreversible thermodynamics, we know that the dissipated Gibbs energy of the discontinuous system is T-ab, where crb here is the entropy production (see Section 4.2). Since dG/dV = dG/dV = crb- T/ A < ), we have with Eqn. (4.8) at the boundary b... 

This equation gives the relation between the electrical potential difference between the copper wires attached to the electrodes when the cell is at equilibrium and the change of the Gibbs energy for the change of state that would take place in the cell if the cell were short-circuited. We point out here that the chemical potentials of electrons refer to 1 mole of electrons or 1 faraday of electricity. Therefore, A G refers to the change of state per faraday. If the change of state requires n faradays,... 

As we have seen in the preceding chapter, the standard thermodynamic properties of species in aqueous solutions are functions of ionic strength when they have electric charges. Substituting equation 3.6-3 for species j and for H + in equation 4.4-9 yields the standard transformed Gibbs energy of formation of species j as a function of pH and ionic strength at 298.15 K ... 

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