Arrhenius hypothesis

All Arrhenius acids contain hydrogen i n their formula and produce hydronium ion (H30 ) in aqueous solution. All Arrhenius bases produce hydroxide ion (OH ) in aqueous solution. Neutralization occurs when each H30 ion combines with an OH ion to form two molecules of H2O. Chemists found the reaction of any strong base with any strong aci d always produced 56 kJ/mol (A/y = —56 kJ/mol), which was consistent with Arrhenius hypothesis describing neutralization. 18.4 Strong acids and bases dissociate completely into ions when dissolved... 

In contrast, the force of interaction between two ions is long-range and at large distances is proportional to 1/r, where r is the distance between the ions. Thus the solution cannot be considered to be composed of noninteracting clusters, and power series expansions in concentration are not possible. Statistical mechanical treatments of this problem demonstrate that the coefficients of the power series expansions diverge for coulomb forces and that another representation for the properties of the solution must be found. The rigorous molecular considerations confirm the results of the Debye-Huckel treatment for dilute solutions and demonstrate that the assumptions of the Arrhenius hypothesis are incorrect. 

In order to formulate the statistical problem generally, let us return to the Arrhenius graph (Figure 5) and ask the question of how to estimate the position of the common point of intersection, if it exists (162). That is, in the coordinates x = T and y = log k, a family of 1 straight lines is given with the slopes bj (i = 1,2,..3) and with a common point of intersection (xq, yo). The ith line is determined by mj points (m > 2) with coordinates (xy, yjj) where j = 1,2,..., mj. Instead of the true coordinates yy, only the values yy = yy + ey are available, ey being random variables with a zero average value and a constant variance,. If the hypothesis of a common point of intersection is accepted, ey may be identified with the experimental error. 

Of course, Sqo Sq if the difference is significant, the hypothesis of a common point of intersection is to be rejected. Quite rigourously, the F test must not be used to judge this significance, but a semiquantitative comparison may be sufficient when the estimated experimental error 6 is taken into consideration. We can then decide whether the Arrhenius law holds within experimental error by comparing Soo/(mi-21) with 6 and whether the isokinetic relationship holds by comparing So/(ml — i— 2) with 5. ... 

Arrhenius knew that these ideas were revolutionary. He avoided mentioning ions in his thesis, for fear his examiners would reject the thesis. Even so, his committee gave him the lowest possible passing grade. In desperation, Arrhenius sent copies of his work to famous professors in several countries. Wilhelm Ostwald, a brilliant chemist, recognized the genius of the ion hypothesis and traveied to Sweden to meet Arrhenius. 

The idea that microbes could migrate across the universe was supported by scientists with a worldwide reputation, such as H. von Helmholtz, W. Thomson (later Lord Kelvin) and Svante Arrhenius. This hypothesis was still accepted by Arrhenius in the year 1927, when he reported in the Zeitschrift fur Physikalische Chemie on his assumption that thermophilic bacteria could be transported within a few days from Venus (with a calculated surface temperature of 320 K) to the Earth by the radiation pressure of the sun (Arrhenius, 1927). The panspermia hypothesis, which seemed to have disappeared in the intervening decades, was reintroduced in the ideas of Francis Crick (Crick and Orgel, 1973). It still exists in a modified form (see Sect. 11.1.2.4). 

Elisabeth Crawford, "Arrhenius, the Atomic Hypothesis, and the 1908 Nobel Prizes in Physics and Chemistry," Isis 75 (1984) 503522. 

Among physicists, Clausius was directly influenced by Williamson s ideas about motion and equilibrium to argue that small portions of an electrolyte decompose even in the absence of an electric current and that there is a dynamic equilibrium between the decomposed and undecomposed species.47 Arrhenius took this hypothesis into an even more radical direction, stating that electrolytes exist in solution as independent ions, while van t Hoff used ideas about mobility and kinetics to develop what he called a "chemical dynamics." Just as chemical questions were influential in starting off these developments in what became the new physical chemistry, so the problem of chemical affinity was central to the origins of modem chemical thermodynamics. 

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. 

We now have seven candidates, and the phase rule allows seven phases to be stable together. We shall state as a working hypothesis that these seven phases—(1) aqueous solution, (2) quartz, (3) kaolinite, (4) hydromica (illite) (5) chlorite, (6) montmorillonite, and (7) phillip-site—are the stable assemblage in the intermediate model, and we shall test this hypothesis against various evidence. Some of these phases may prove unstable and be replaced by some other phase—e.g., phillipsite by another zeolite or a feldspar. Chlorite might also be replaced by some of the magnesium silicates described by Arrhenius (3). 

Arrhenius (1889) put forward the hypothesis that all the molecules of a reactant do not take part in the chemical reaction. It is only a certain number of molecules known as active molecules that may take part in the reaction. 

It should be noted that the temperature gradient in the front at 4.2 K is about 2 times that at 77 K (see Fig. 8), that is, the degree of chemical conversion increases with decreasing initial temperature. This is also atypical of the thermal mechanism based on the Arrhenius law, but can be explained by the above hypothesis, considering that the lifetime of a new surface in the active state increases with decreasing temperature, which results in the enhanced conversion. 

In 1887 Svante Arrhenius advanced the then very revolutionary hypothesis that many salts dissolved in aqueous solutions ionize partially or completely. Such a process may be... 

Anodic aluminum oxide, 312, 401 Antiferromagnetic-like interactions, 141 Antiferromagnetism, 433 Arc discharge method, 448 Ar ion sputtering, 449 Arrhenius, Carl Axel, 4 Arrhenius-Uke behaviour, 134 Asteriod hypothesis, 46 Atomic force microscope (AFM), 397 Atomistic simulation, 296,297 Au(llO), 137 Au(lll), 135... 

Arrhenius in 1887 had suggested that many properties of electrolytes could be explained by a dissociation hypothesis The neutral molecules AB of the electrolyte dissociate to form ions A and B , and this dissociation is governed by an equilibrium... 

In 1884 Svante Arrhenius advanced the then very revolutionary hypothesis that salts dissolved in aqueous solutions tend to ionize partially or completely. Such a process may be represented by an equation of the form Mv Ai, (aq) = v i M + -1- v A - where M and A represent the cationic and anionic constituent of the compound, z+ and z- are their appropriate ionic charges and y+ and v, the stoichiometry numbers. The ionization process symbolized above requires that My Ay itself be considered either as a dissolved species that may be equilibrated with the undissolved compound in a saturated solution or that exist as such. This formulation also hides a multitude of difficulties in many cases the ionization process is much more complex than indicated above. For example, in the ionization of Agl one encounters in aqueous solution the species Agl, Ag+, I , Agl2, Ag2l", and several more exotic combinations. In what follows we limit ourselves to cases where there is a great preponderance of the elementary species over the more complex aggregates. 

Subsequent research has entirely confirmed the theory of Arrhenius. The chemical and electrochemical behaviour of solutions is closely connected with their ionic dissociation, and would be quite inexplicable without this theory. Rarely in the history of science has an idea proved so fruitful and suggestive, and led to the discovery of so many hitherto unsuspected relationships as this hypothesis of Arrhenius. 

On the whole hypothesis (1) appears to be the correct one 1 It will be observed that in the treatment here followed we are not considering the more recent investigations of Ghosh, Bjerrum and others who have come to the conclusion that in solutions of strong electrolyte dissociation is complete and therefore the Arrhenius expression is incorrect... 

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