Endoergic

The previous treatment applies to exoergic chemical reactions (with positive energy difference between the minima of the initial and final states AE = — > 0)- For endoergic reactions... 

The PES found by Smedarchina et al. [1989] has two cis-form local minima, separated by four saddle-points from the main trans-form minima. The step-wise transfer (trans-cis, cis-trans) - because of endoergicity of the first stage - displays Arrhenius behavior even at T < T. . The concerted transfer of two hydrogen atoms was supposed to become prevalent at sufficiently low temperatures. However, because of too high a barrier for the concerted trans-trans transition, this... 

Endothermic Also called endoergic. Pertaining to a reaction which absorbs heat. 

An empirical solution of Eq. (1) consists of analysis of the solvation process of the target molecule in solute, finding descriptors, which govern each phase and using them to calculate logP. This was done, for example, in the LSER approach which considered that the process of any solvation involves (i) endoergic creation of a cavity in the solvent and (ii) incorporation of the solute in the cavity with consequent setting up of various solute-solvent interactions [4—6]. Each of these steps... 

This energy is consumed to overcome the overpotentials of the electrode reactions (rja, rjc), the IR drop in the external circuit and electrolyte, and it might partly be converted into the free energy, AG, of stable products (if any) of the endoergic electrochemical reaction ... 

In conclusion, under the hypothesis that the reaction has no barrier in excess of its endoergicity, Att/°j(0) = 0, the enthalpy of reaction 3.10 is given by the Arrhenius activation energy for the forward reaction minus a heat capacity term. This term can be estimated by using statistical mechanics, provided that a structure for the activated complex is available. It is often found that T A Cjj > is fairly small, ca. — 1 kJmol-1 at 298.15 K [60], and therefore, the alternative assumption of a,i Ar//" is commonly accepted if T is not too high. Finally, note that either 3,1 Ar//." or Atf/°j(0) = 0 are not equivalent (see equation 3.22) to another current (but probably less reliable) postulate, Ea- = 0. 

A change in a system or chemical reaction for which there is an absorption of heat (i.e., the process requires heat to proceed). In such systems, AH is a positive value (where H is the enthalpy). See also Enthalpy Exothermic Endogonic Endoergic... 

ENDOPOLYGALACTURONIDASE ENDOPOLYPHOSPHATASE Endoskeleton and exoskeleton, BIOMINERALIZATION ENDOTHERMIC PROCESS ENTHALRY EXOTHERMIC ENDOGONIC ENDOERGIC ENDOTHIAPEPSIN Endo-1,4-/J-xylanase,... 

When Q is absorbed it is given negative sign and the reaction is known as endoergic. For example,... 

The expression for Keq in (8.27d) shows that if AG° < 0 ( exoergic ), then Keq > 1, and the reaction lies toward the product side at equilibrium. Conversely, if AG° > 0 ( endoergic ), then Koq < 1, and equilibrium lies toward the reactant side. 

Note that if Q is positive, the reaction is exoergic while if Q is negative, the reaction is endoergic. Thus, the sign convention for Q is exactly the opposite of the familiar AH in chemical reactions. A necessary but not sufficient condition for the occurrence of a nuclear reaction is that... 

Endoergic Reactions (Electronically and Vibrationally Excited States)... 

As a general rule, the rates of those reactions that are endoergic for ground-state reactions are dramatically enhanced when excited-state reactants are employed. Electronic excitation and vibrational excitation may or may not have similar effects. In the case of vibrational excitation, the reactions may occur on a single electronic potential surface. In the case of electronic excitation, a single-surface path between electronically excited reactants and ground-state products may not exist because of the prevailing symmetries. 

All these reactions are exothermic for the metastable 02+ (a%u) state. As the corresponding ground-state reactions, are endoergic, all have negligibly small rate coefficients (< 10 12 cm3/sec) over the same translational-energy range. 

Many dissociative charge-transfer reactions6 that are endoergic for ground-state ions also become energetically allowed for some electronically excited state of the reactant ion. For example, the reaction of excited Kr + ions with methane has been observed18,19... 

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