The Phenomenon of Compensation

It is said that In argument there is much heat but little light , and its truth is amply verifled by the extensive literature on compensation phenomena for on no other subject in the field of catalysis has so many words been expended to such little purpose. The experimental observation is in essence very simple in a series of catalysts or reactions sharing a common feature there is often observed a linear correlation between activation energy and pre-exponential factor, of the form 

This relation was first observed by FH. Constable in 1925, and was subsequently noted by G.-M. Schwab, who was the first to use the term compensation , and 

It is also important to note that the most active catalyst of a group is only that with the lowest activation energy when measurements are made below Ti above this temperature, the opposite is tme, thus negating the commonly held (and taught) correlation of activity with a lowering of activation energy, which is (as the Arrhenius equation shows) not the sole determining factor. 

The phenomenon of compensation is not unique to heterogeneous catalysis it is also seen in homogeneous catalysts, in organic reactions where the solvent is varied and in numerous physical processes such as solid-state diffusion, semiconduction (where it is known as the Meyer-Neldel Rule), and thermionic emission (governed by Richardson s equation ). Indeed it appears that kinetic parameters of any activated process, physical or chemical, are quite liable to exhibit compensation it even applies to the mortality rates of bacteria, as these also obey the Arrhenius equation. It connects with parallel effects in thermodynamics, where entropy and enthalpy terms describing the temperature dependence of equilibrium constants also show compensation. This brings us the area of linear free-energy relationships (LFER), discussion of which is fully covered in the literature, but which need not detain us now. 

Much trouble has been taken to find statistical criteria that will establish the 

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Again we feel that a rationale for correct results from incorrect input information may be found in the phenomenon of compensating errors such as have already been shown to minimize the effects of differences between arbitrary and ruby N, M, and Q in Eq. (1). It is no less likely that, even where the computer grossly misjudges the AVs, the buffered equilibria may introduce mutual cancellations which also tend to lessen the effects on ruby s pressure and velocity of errors in the various quantities which interact to produce these predictions in the computer s multi-iterative machinations. Thus relatively large differences between ruby values and actual values of pj, Pt (or Vg), T, the Atf/s, CvdT., N, < , Ej—Eo, y,... 

It would be tedious and of no great value to review the many and varied attempted explanations of the phenomenon of compensation (see Further Reading), because as we shall see shortly, they may be wide of the mark at least as far as reactions of hydrocarbons go. There are however a number of review articles that may be consulted if desired. On reflection however it seems more fruitful to focus attention on the reason for the variation in the activation energy, and perhaps... 

The phenomenon of the contrast enhancement is caused by side-directed diffusion of silver atoms into the exposed areas because of the decrease of chemical potential in the areas. Silver atoms diffusion from the unexposed areas into the exposed ones compensates the influence of diffraction effects. As a result of diffusion, resolution may be considerably improved. 

The phenomenon of rigidification can be interpreted both as the result of degradation of the PC and as a consequence of the loss of additives designed to plasticize the macromolecules. In both cases, any outdoor use of parts made of recycled PC must be preceded by a stage of reformulation to compensate for the loss of the stabilizing and plasticizing additives present in virgin PC. 

The building subcontractor referred to above was evidently involved in an active and deliberate process of claims suppression in order to maintain his near perfect compensation record and his low compensation premium. At times, however, the phenomenon of claims suppression is more complex it may result from the simultaneous operation of a number of influences, with employer interest in minimising compensation costs only an implicit factor. 

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