Critical increment

Activation of molecules with many degrees of freedom energy of activation and critical increment . 

For this reason the constant of the Arrhenius equation is sometimes called the critical increment of energy. When n is small E and E-U are very nearly equal. ... 

For the analysis of vital activities it seemed, then, that the critical thermal increment might assist in the classification of inner processes even though no definite identification of the chemical transformations concerned might be possible. As it happens, however, the analysis can in reality be pushed much further than this. A difficulty arises from the fact that on either side of a certain temperature (frequently 15° = =) the value of the critical increment is different. This discovery is especially significant for the understanding of the variability of protoplasmic activities and of the basis of adaptation. The fact itself is taken to signify that the velocities of vital phenomena are controlled by catenary series of reac-... 

Beyond this, it is found that some 19 distinct physiological processes the velocities of which have been measured by various workers over ranges of temperature, and for which one has in some instances direct evidence for dependence upon cell respiration, yield sensibly identical values of the constants fjL, Whereas with processes obviously different (for example fermentation, and photosynthesis) the critical increments are unquestionably in different categories. 

Noyes Vaughan (Ref 5) investigated thermal, electronic and photochemical decompns of solid bodies, among them some expls. They found that in many cases where the rate of thermal decompn can be detd without ambiguity, the variation with temp is satisfactorily given by the Arrhenius equation K=Ae, where K is the specific reaction rate, A is a constant, E "the heat of activation , (the critical increment per gram-molecule), R the gas constant per g mol per °C and T the absolute temp... 

Thermal Decomposition of LA has been the subject of study by a large number of investigators Hitch (Ref 17) found LA extremely hard to decomp without explg. Garner Gomm (Ref 44) in studying the rate of de-compn of a and /3-fotms found that jS-LA de-compd much more rapidly than o-LA the critical increments were tt-form 47,600 cals and /3-form 38,800 cals. The kinetics of... 

Using 25,000 as the approximate critical increment, this gives at 30.1°C. the following comparison ... 

In any event it is not to be confused with the change found by Hirst and Rideal as it is not even of a comparable magnitude. Furthermore, a six-to one-hundred fold variation in the initial concentration of the pentoxide produces no appreciable change in the average velocity constant. Last of all the critical increment calculated from the measured velocity constants, 0.0044 at 30.1°C. and 0.0162 at 40.0°C. yields the following result ... 

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