Linear reversible region

Irreversible If i > 0, i.e., departure from equilibrium, situation is irreversible in the thermodynamic sense. If Iql < RT/F, reaction is in reversible region and there is a linear relation of / to q Uses phrase totally irreversible" for Iql > RT/F Tafcl region... 

Finally, for currents close to the diffusion-limiting current (very cathodic potentials), a new linear region appears (labeled 3 in Fig. 3.7) which, for a = 0.5, presents the same slope as the reversible region. The linear dependence found here can be identified using a truncated asymptotic expansion of function F given by Eq. (E.9) of Appendix E... 

Fig. 4L Variation of the peak potential for an anodic process with sweep rate over a wide range, covering both the reversible and the linear Tafel regions. The "critical" sweep rate v is the...

This is usually called the "totally irreversible case", but we consider the term to be misleading because, as seen in Fig. JL, the reaction can, in fact, be reversed. Referring to it as the "linear Tafel region" implies that the reaction occurs at high overpotentials, where the rate of the reverse reaction can be neglected. 

Since (a/n) is usually smaller than unity, the peak current in the linear Tafel region is, as a rule, smaller than in the reversible region. The difference is not very large, however. For a = 0.5 and... 

Fig. lOL Calculated HE plots during linear potential sweep for mono-layer adsorption, as a function of sweep rate, for = 160 iClcm. The range of sweep rates and rate constants have been chosen so as to show both the reversible and the linear Tafel regions. The Y - axis is given in units of pseudocapacitance, = i/v. Reprinted with permission from Srinivasan and Gileadi, Electrochim. Acta, 11, 321, 1966). Copyright 1966, Pergamon Press. 

Extrapolation of the linear (Tafel) region of the relation between log (current) and the potential to the condition 17 = 0 gives the exchange current density io- This presupposes that the potential corresponding to this condition (17 = 0) is known, i.e., that the reversible potential for the electrode reaction is known or can be determined, e.g., from appropriate thermodynamic data. For many organic electrode processes, however, the required thermodynamic data are not available so that Er cannot be calculated. 

Fig. 11.1 - Tests for a reference electrode. (1) The micropolarisation tests the reversibility of the reaction is examined in the linear /-ry region. Figs (a) and (b) show the response for a good and bad reference electrode respectively. (2) The dependence of potential on anion concentration. Fig. (c) shows the Nernst plot for a good reference electrode.

In the seventeenth century, the British physicist Robert Hooke (Purrington 2009) defined the basic relation between stress and strain as Ut tensio, sic vis. meaning extension is proportional to force. This so called Hooke s law is valid for many inorganic materials in the linear elastic region, where force-induced deformations are reversible and the material will completely return to its initial shape after removing the force without any delay or residual plastic deformations. 

An inadequate intake in the diet of those food chemicals that are essential nutrients results in health risks. Indeed these risks are by far the most important in terms of the world s population where malnutrition is a major public health problem. But, unlike the toxic chemicals, they would show a very different dose-response if they were subject to similar animal bioassays. At very low doses there would be a high risk of disease that would decrease as the dose was increased, the curve would then plateau until exposure was at such a level that toxicity could occur. Figure 11.2 shows this relationship which is U- or J-shaped rather than the essentially linear dose-response that is assumed for chemicals that are only toxic. The plateau region reflects what is commonly regarded as the homeostatic region where the cell is able to maintain its function and any excess nutrient is excreted, or mechanisms are induced that are completely reversible. 

Thus, while the relation between the partial current densities and potential is exponential, in the region of low polarization a linear relation is obtained between polarization and the net CD, owing to a superposition of the currents of forward and reverse process. At A = 10 mV, the error introduced by the approximation above will be between 1 and 20%, depending on the relative values of a and p it becomes even smaller with decreasing polarization. Hence we can by convention consider the interval of polarization values between -10 and 10 mV as that of low polarization where the linear relation (6.6) is valid. 

As the redispersion region may be the result of a charge reversal, the electrophoretic mobilities of the MCC sols as a function of NaCl concentration were determined. No charge reversal was detected and the mobility of the particles decreased from 3.5 to 2.6 mobility units in a linear manner with increasing salt concentration indicating that the redispersion region was not caused by charge reversal. 

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