Exothermic gap

Intertidal bivalves have been used extensively to study bioenergetic responses of organisms to oxygen limitation. Of particular note is the excellent series of papers on the bay mussel Mytilus edulis [10,12,35,58,59], which soundly established the utility of calorespirometry and provided an excellent experimental data base and theoretical concepts for future testing. Useful reviews of this work exist [3,13], so 1 will not reevaluate the work and its implications here, except to point out that the studies contributed to, among other issues, the ongoing debate over the existence of an anaerobic exothermic gap in invertebrates (see section 3.2)... 

At this juncture, based on the work with M. edulis, S. nudus and H. medicinalis, a statistically significant exothermic gap cannot be measured during early phases of anoxia (i.e., <24 h). However, with increased anoxic duration, an exothermic gap is measurable in M. edulis and H. medicinalis (extended periods of anoxia have not been evaluated in this context with S. nudus). For T. tubifex an exothermic gap is perhaps measurable within a 20 h period of anoxia, if the re-evaluation of Gnaiger and StaudigI [20] is followed. Clearly interspecific differences exist, and the experimental duration of anoxia used is an important determining factor. It appears that an exothermic gap is present in certain cases. The implication is that additional biochemical events that are not thermally-neutral must still be evaluated in order to obtain a complete enthalpy balance for all species. 

Jortner, J. Navon, G. J. Phys. Chem. 1981, 85, 3759]. On the other hand, if one considers the variation of activation energy with electronic energy gap, one finds a very large discrepancy between the quantum-mechanical and classical approaches for very exothermic reactions at room temperature (see Figure 1). 

Information gained from simulations can reveal key insights that explain gaps or contradictions in information. The time line is a useful tool in this development. For incidents of unexpected chemical reactions, it is common to attempt a lab scale simulation of the conditions involved in the exotherm or explosion. Many chemical processes can be modeled and duplicated dynamically by computer algorithms. Accelerated rate calorimeters (ARC) have proven to he highly useful tools for studying exothermic or overpressure runaway reactions. 

Fig. 5.15 Decomposition of thermaiiy degraded GAP, showing that the exothermic peak decreases as the mass fraction of degradation is increased.

When AN particles are mixed with GAP, AN-GAP composite propellants are formulated. The specific impulse is increased by approximately 10 s by replacing PB or PU binder with GAP, as shown in Fig. 4.16. The burning rate is also increased due to the exothermic decomposition of GAP. Since GAP burns by itself, the burning of the AN particles is supported by the exothermic decomposition reaction of the GAP at the burning surface of the propellant. As shown in Fig. 7.61, the burning rate is drastically decreased by the addition of AN particles. When is in-... 

The results of thermochemical experiments reveal that an exothermic reaction of GAP occurs at about 526 K and that no other thermal changes occur. When Mg or Ti parhcles are incorporated into GAP to formulate Mg-GAP or Ti-GAP pyrolants, two exothermic reactions are seen the first is the aforementioned exothermic decomposihon of GAP, and then a second reachon occurs at 916 K for the Mg-GAP pyrolant and at 945 K for the Ti-GAP pyrolant There is no reaction between either Mg or Ti and GAP at the temperature of the first exothermic reaction. Both Mg and Ti particles within GAP are ignited by the heat generated by the respechve second exothermic reactions. 

However, no MgO is seen in the residue, indicating that this compound is not produced by reaction between Mg and CO. On the other hand, no TiN is seen in the residue of the Ti-GAP pyrolant, implying that there is no reaction between Ti and Nj to produce this compound. Ti particles react exothermically with carbon formed by the decomposition of GAP according to ... 

If AEt is about 1000 cm-1 (2.86 kcal), then ke is faster than k.e by a factor of 100. Thus the axiom that triplet energy transfer is efficient only when it is exothermic by at least 3 kcal arises because an energy gap of this size is needed to eliminate back transfer. In fact, forward energy transfer is moderately efficient even when it is slightly endothermic. (Note the rate values for 1,5- and 1,8-dinitronaphthalene where transfer is about 0.3 kcal endothermic.)... 

Fig. 4. The scheme of electron bands in a semiconductor. 1, Impurity level located near the bottom of the conduction band 2, 3, impurity levels located near the top of the valence band. Ie is the electron ionization energy, Ih is the hole ionization energy, and Es is the width of the forbidden gap. The exothermal electron transfer reaction in the vicinity of the top of the valence band is shown by the arrow.

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