Reversible and Irreversible Work

The distinction between reversible and irreversible work is one of the most important in thermodynamics. We shall first illustrate this distinction by means of a specific numerical example, in which a specified system undergoes a certain change of state by three distinct paths approaching the idealized reversible limit. Later, we introduce a formal definition for reversible work that summarizes and generalizes what has been learned from the path dependence in the three cases. In each case, we shall evaluate the integrated work w 2 from the basic path integral, 

The system chosen for this example consists of a spring and attached platform (Fig. 3.1). The surroundings consist of an assortment of weights (totaling 1000 g) and a vertical 

Let us now assess the work performed in each path. In path (a), no weights were lifted, and therefore no work was performed  

Definition A reversible path is a limiting process in which every point of the path is an equilibrium point, so that only an infinitesimal amount of work is sufficient to reverse the path. 

For the irreversible paths (3.3a-c), the system was out of equilibrium (Fspring Fgravity) at many points, whereas the limiting reversible path is characterized by perfect force balance 

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Example Reversible and Irreversible Work. In an isotropic elastic body the following equation holds (Landau et al. 1986) ... 

Palladium hydride is a unique model system for fundamental studies of electrochemical intercalation. It is precisely in work on cold fusion that a balanced materials science approach based on the concepts of crystal chemistry, crystallography, and solid-state chemistry was developed in order to characterize the intercalation products. Very striking examples were obtained in attempts to understand the nature of the sporadic manifestations of nuclear reactions, true or imaginary. In the case of palladium, the elfects of intercalation on the state of grain boundaries, the orientation of the crystals, reversible and irreversible deformations of the lattice, and the like have been demonstrated. 

Thermodynamically, the fracture energy is the sum of the reversible work (fF representing the reversible molecular interactions at the interface) and irreversible work (fVi, representing the irreversible deformation of the interfacial joint) both W, and fVi are expressed per unit area of the fracture energy by Eq. (9). 

Acetylcholinesterase is subject to substrate Inhibition at high concentrations, but Mlchaells kinetics are observed at lower concentrations, because the substrate constant and the Mlchaells constant differ by a factor of 100. Turnover numbers run about 2-9 x 10 min l, and (Mlchaells constant) values are about 0.2 mM.76,116 Whatever the source, the enzyme is subject to inhibition by the same reversible and irreversible inhibitors. Most of the kinetic work has been done with the saline-extracted 11S enzyme from electric eel and the detergent-extracted 6S enzyme from erythrocytes. The former Is a tetramer derived from the native enzyme by the action of proteases the latter is a dimer. 

Small-molecule inhibitors of caspases would have obvious use as therapeutics. The current medicinal chemistry research literature is rich in studies attempting to achieve this important design goal. In early work, both reversible and irreversible peptide-based inhibitors of various caspases have been developed. Peptidomimetic ketones were also devised for example, acyloxymethyl ketones were designed and developed as potent, time-dependent irreversible caspase inhibitors. 

TABLE 3.1 Comparison of Reversible and Irreversible Gas Expansion with Respect to Equilibration, Reversibility, Rate, and Work Capacity... 

Electrochemical irreversibility is caused by slow electron exchange of the redox species with the working electrode. (The reader is referred to Chap. 2 for a discussion of irreversibility.) In this case Equation 3.25 is not applicable. Electrochemical irreversibility is characterized by a separation of peak potentials that is greater than 0.059/n V and that is dependent on the scan rate (Examples are given in Chapter 23.) Figure 3.25A illustrates voltammograms for reversible and irreversible systems. 

The thermodynamic basis of the calculation of the maximum possible work potential or chemical exergy of reversible and irreversible chemical reactions is explained and discussed. Combustion is asserted to be fundamentally irreversible. It is a nonequilibrium uncontrollable chain reaction with hot branches, in a cool milieu, and a limited work output proportional to Carnot efficiency x calorific value (Barclay, 2002). 

To show that the individual de are nonnegative consider some spontaneous process for which dsm < 0 and examine the consequences by comparing work performance in reversible and irreversible processes. 

The borderlines between reversible, quasi-reversible, and irreversible behavior were originally defined by Matsuda and Ayabe [12] on the basis of mathematical reasoning. However, in practical work it is more convenient to define borderlines reflecting where deviations from the two limiting cases, reversible and irreversible, may be observed experi-... 

FIGURE 13.7 Work done by a system in reversible and irreversible expansions between the same initial and final states. The work performed is greater for the reversible process. 

This theoretical model has been applied, mainly in very recent work [94], to correlating the behaviours of diverse reactants. It is too early to assess the impact that this approach may have on the development of the subject, but the work offers positive prospects for stimulating debate. The model has been applied to reversible and irreversible, endothermic and exothermic decompositions and is an alternative to the Polanyi-Wigner treatment (Section 4.5.) with which it shares some very... 

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