Electrical work, from chemical

One of the oldest and most important applications of electrochemistry is to the storage and conversion of energy. You already know that a galvanic cell converts chemical energy to work similarly, an electrolytic cell converts electrical work into chemical free energy. Devices that carry these conversions out on a practical scale are called batteries1. In ordinary batteries the chemical components are contained within the device itself. If the reac-tantsare supplied from an external source as they are consumed, the device is called a fuel cell. 

This amount of work is substantially less (often three to five times less) than could be obtained electrochemically from the same reaction. Thus the electrochemical cell offers possibilities for efficient production of electrical energy from chemical sources that are unequalled by any other device. 

HAZARD means an3dhing that can cause harm (e.g. chemicals, electricity, working from ladders, etc) ... 

Ions play a key role in many thermodynamic systems. Because ionic solutions can carry a current, chemical changes not considered in previous chapters might occur spontaneously. Some of those changes are very useful, because we can extract electrical work from those systems. Some of these changes are spontaneous but not inherently useful. For example, corrosion is one electrochemical process that is by definition an undesirable... 

Now if the chemical reaction had been allowed to proceed without the performance of any external electrical work, say in a calorimeter, so that the initial and final temperatures of the system are both T, the change of intrinsic energy would have been the same as that occurring in the process described above, as we know from the First Law. Thus the heat of reaction, Q will be equal to the increase of intrinsic energy ... 

The total inapplicability of the Thomson rule to this case is at once apparent none of the electrical energy comes from chemical change, but the cell functions as a heat engine, converting the heat of its environment into electrical work. 

Figure 9.3 The lead storage battery. The key to obtaining electrical energy from a redox chemical reaction is to physically separate the two half-cell reactions so that electrons are transferred from the anode through an external circuit to the cathode. In the process, electrical work is accomplished.

Electrochemical redox studies of electroactive species solubilized in the water core of reverse microemulsions of water, toluene, cosurfactant, and AOT [28,29] have illustrated a percolation phenomenon in faradaic electron transfer. This phenomenon was observed when the cosurfactant used was acrylamide or other primary amide [28,30]. The oxidation or reduction chemistry appeared to switch on when cosurfactant chemical potential was raised above a certain threshold value. This switching phenomenon was later confirmed to coincide with percolation in electrical conductivity [31], as suggested by earlier work from the group of Francoise Candau [32]. The explanations for this amide-cosurfactant-induced percolation center around increases in interfacial flexibility [32] and increased disorder in surfactant chain packing [33]. These increases in flexibility and disorder appear to lead to increased interdroplet attraction, coalescence, and cluster formation. 

The free energy functions are defined by explicit equations in which the variables are functions of the state of the system. The change of a state function depends only on the initial and final states. It follows that the change of the Gibbs free energy (AG) at fixed temperature and pressure gives the limiting value of the electrical work that could be obtained from chemical transformations. AG is the same for either the reversible or the explosively spontaneous path (e.g. H2 -I- CI2 reaction) however, the amount of (electrical) work is different. Under reversible conditions... 

Fig. 6.44. A thought experiment for the definition of the chemical potential p. An uncharged solution without an oriented-dipole layer on its surface is taken. The work done to transport a unit of positive test charge from infinity into the interior of the phase is the chemical potential p of the phase. The electrical work = xy + x is zero because there is no charge and no oriented-dipole layer on the surface of the solution.

The electrochemical potential of the charged species i in a given phase contains terms originating from both the electrical and the chemical work. Thus, for the electrochemical potential of charged species i in the electrode we can write... 

Most of our available energy is obtained indirectly from chemical energy. In the steam turbine, the generation of mechanical work proceeds through pathway I (Figure 9.1) and includes heat and electrical energies, whereas that... 

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