Number stoichiometric arithmetic

Dobereiner showed (mentioning Dalton) that atmospheric air is not a compound. He pointed out that the equivalent of strontiiun (42 5) is the arithmetic mean of those of calcium (20) and barium (65), and in 1829 he extended this relation (afterwards called the law of triads ) to many other groups of three analogous elements ( Trias ). In 1817 he pointed out that widely distributed elements have small atomic weights (stoichiometric numbers), and that some elements (Fe, Co, Ni, Cr, Mn) have nearly the same atomic weights. He established the identity of chromic acid, which had been questioned by... 

As discussed in the previous chapter, there is an important distinction between the stoichiometric equations that describe the overall arithmetic of a chemical reaction—the relative numbers of molecules that are consumed and produced— and the set of equations that constitute a mechanism for the reaction. A mechanism is composed of a set of reactions called elementary steps, each of which is taken to represent an actual molecular event that leads to the overall reaction. The complete set of elementary steps must yield the correct stoichiometry and the experimentally observed rate law of the reaction. 

By placing all the components in the seeond member, the algebraic stoichiometric numbers, yu, are equal in absolute value to the corresponding arithmetic stoichiometric numbers but are positive for the eonqranents produced by the reaction and negative for reactants. 

Now we will discuss using the rate factors fp for step p from left to right and f" from right to left. It is known that the rate factor [SOU 90, p. 247] of an elementary step p is the product of the rate constant k and the concentrations of the reactants and products of total reaction, which intervene as reactants in the Step p and each one raised to the power of their arithmetic stoichiometric number p. A rate factor depends on the temperature via the corresponding rate constant. The factor fp is thus constant if we work at a constant temperature and with constant concentrations of the main reactants and products. 

This chemical equation, besides the chemical species being involved, includes numbers placed in front of each species (e.g. 2 for N2) that are called the arithmetic stoichiometric coefficients. The set of coefficients belonging to a reaction may be multiphed or divided by the same number without modifying the reaction in any way. For example, the above reaction could also be written by multiplying all the stoichiometric coefficients by two in the following ... 

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