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Related to Reactivity: Reactivity series


The relative capacity of an atom, molecule, or radical to combine chemically with another atom, molecule, or radical.
A measure of the deviation of a nuclear reactor from the critical state at any instant of time such that positive and negative values correspond to reactors above and below critical, respectively; measured in percent k, millikays, dollars, or in-hours.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



a measure of the chemical activity of substances accounting for the variety and rate of the reactions possible for a given substance. For example, noble metals (Au, Pt) and inert gases (He, Ar, Kr, Xe) are chemically inactive; that is, they possess low reactivity. Alkali metals (Li, Na, K, Cs) and halogens (F, Cl, Br, I), on the other hand, are chemically active; that is, they possess high reactivity.

In organic chemistry, alkanes are characterized by low reactivity and therefore can undergo only reactions (radical halo-genation and nitration, dehydrogenation, dissociation with rupture of C—C bond) occurring under such vigorous conditions as elevated temperatures and ultraviolet irradiation. For the alkyl halides, additional reactions, such as dehydrohalogen-ation, nucleophilic substitution for the halogen, and the formation of organomagnesium compounds, are possible under mild conditions. The presence of double or triple bonds or functional groups (hydroxyl —OH, carboxyl —COOH, amino —NH2) in a molecule promotes a further increase in reactivity.

Reactivity is quantitatively expressed by specific rate constants or, in the case of reversible processes, by equilibrium constants. Modern concepts of reactivity are based on the valence-bond theory and on the study of the distribution (and displacement upon action of a reagent) of the electron density in a molecule. Electron displacements are defined qualitatively through inductive and mesomeric effects and quantitatively through quantum-mechanical calculations. The key factor determining the relative reactivity of a number of related compounds is the molecular structure, which encompasses the nature of the substituents, the electronic and steric effect of these substituents on the reaction center, and the geometry of the molecule. Reactivity is dependent on the reaction conditions, for example, the nature of the medium, presence of catalysts or inhibitors, pressure, temperature, and irradiation. Depending on the mechanism of a given reaction, these factors all have a varied and sometimes contrary effect on the reaction rate. The quantitative relationship between rate (or equilibrium) constants within one reaction series may be represented by correlation equations, which describe the change in the constant as a function of the change in a given parameter. Examples are seen in the Hammett-Taft equation, which deals with the effect of a substituent, and the Brønsted equation, which deals with solvent polarity.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Time-temperature reactivity evaluations were used as the initial method of analysis.
Table 1 summarizes the comparison of results of comparison of autonomic reactivity parameters - IHG and deep breathing (E/I) ratio in subjects before and after consumption of aspartame diluted in water.
It also exhibits the desirable prospect of benefiting future studies aimed at understanding the chemical reactivity of the colored products with larger molecular weights that are obtained when reducing sugars react with proteins and peptides.
The void reactivity feedback in this study was estimated using two moderator density profiles provided by [6].
Immune Reactivity between Monoclonal Anti-Insulin and Anti-Insulin Receptor
Immune Reactivity between Affinity-Purified Polyclonal Antibodies and Food Antigens.
It was concluded that sucrose, trehalose and BSA have considerable effects on the specific reactivity of anti rHBsAg mAbs during long storage.
In the pre- and post-intervention assessment, cognitive reactivity to sad mood was assessed using the revised Leiden index of depression sensitivity scale.
It is possible that this high degree of nonspecific reactivity may be related to particular staining conditions in our laboratory, because in the two prior publications nonspecific reactivity of p-Napsin A in mucinous carcinomas was significant but not universal.
The effectiveness of boric acid [[rho].sub.b] ([C.sub.b]) at concentration [C.sub.b] represents the value of reactivity, that the reactor loses while increasing the boric acid concentration in the coolant from 0 to [C.sub.b]:
Fe/Fe-oxide MNPs synthesized in our laboratory have showed the enhanced reactivity towards targeted contaminants due to the presence of zero valent iron (ZVI) protected by a passivated oxide shell.

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