Permissive substitution laws

States generally have one of two types of substitution laws permissive substitution laws and mandatory substitution laws. Mandatory substitution... 

Fi gu re 4.3. Plot of nonradiative decay constants for an homologous series of Re(bpy)(CObX (X = pyridine or substituted pyridine). The observed lifetime is dose to I /knr. The solid line is the best theoretical fit with the energy gap law. (Reprinted from Ref. 13 with permission. Copyright 1990 American Chemical Society.)... 

Quoting Cornille [87, p. 168] The calculation concerning the electromagnetic conservation laws given in most textbooks, for example, in Jackson [7, p. 239] is not correct, as noted by Selak et al. [88], because it is not permissible to substitute a convective time derivative for an Eulerian time derivative even when we have a constant volume of integration. ... 

According to the last equation the activities of gases at infinitely low pressures can be substituted in the equation of the law of mass action by corresponding partial pressures. It has been shown that such a substitution is permissible even at middle low pressures (i. e. about 1 atm.) provided the temperature of the gas is sufficiently above its temperature of liquefaction. Unless this condition is satisfied the activity of gases must bo substituted in principle by the product of their partial pressures and corresponding activity coefficients according to equation (V-16). 

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