Formal chemical species

Imagine further burning of gaseous sulphur. Gaseous sulphur can be present in different (polyatomic) configurations, but this information is either unknown or irrelevant we thus regard sulphur as formal chemical species S. We then have the reaction scheme... 

Let us now consider one of the phases, thus a region in space occupied by a continuous multicomponent mixture. The actual nature (molecular configuration) of the mixture may be little known imagine, e.g., a liquid ionic solution with various degrees of dissociation, solvatation, etc. One then usually assumes that some equilibria (such as ionic equilibria) are installed very rapidly so that the (instantaneous local) thermodynamic state at a point of the mixture can be defined by the temperature, pressure, and mass (or mole) fractions of certain K components C, —, . The Q are some formal chemical species the... 

Both molarity and formality express concentration as moles of solute per liter of solution. There is, however, a subtle difference between molarity and formality. Molarity is the concentration of a particular chemical species in solution. Formality, on the other hand, is a substance s total concentration in solution without regard to its specific chemical form. There is no difference between a substance s molarity and formality if it dissolves without dissociating into ions. The molar concentration of a solution of glucose, for example, is the same as its formality. 

Normality is the number of equivalent weights (EW) per unit volume and, like formality, is independent of speciation. An equivalent weight is defined as the ratio of a chemical species formula weight (FW) to the number of its equivalents... 

Chemical reactions can often formally be expressed as the sum of two or more "half-reactions in which electrons are transferred from one chemical species to another. Conventionally these are now almost always represented as equilibria in which the forward reaction is a reduction (addition of electfons) ... 

In the last two sections the formal theory of surface thermodynamics is used to describe material characteristics. The effect of interfaces on some important heterogeneous phase equilibria is summarized in Section 6.2. Here the focus is on the effect of the curvature of the interface. In Section 6.3 adsorption is covered. Physical and chemical adsorption and the effect of interface or surface energies on the segregation of chemical species in the interfacial region are covered. Of special importance again are solid-gas or liquid-gas interfaces and adsorption isotherms, and the thermodynamics of physically adsorbed species is here the main focus. 

Formally, we are free to choose any linear combination of the three chemical species as the reacting scalar under the condition that the combination is linearly independent of the rows of A.12 Arbitrarily choosing C3, a new scalar vector can be defined by the linear transformation13... 

Chemical Species Balances Decay Factors for Reactive Species The CEB method can be extended to families of chemical compounds, such as polycyclic aromatic hydrocarbons (PAH), while taking chemical reaction into account. Formally this can be done by writing chemical species balances in a somewhat different fashion from the CEB formulation ... 

The arrangement of ions in the different sites of the perovskite structure (Figure 10) has been described above (Section 2.2). The number of different chemical species which crystallize with this structure (or in a distorted form) is legion. These compositions are listed in two major compilations (Refs. 169 and 170). The large A cation normally carries a low formal oxidation state, such as mono-, di-, or tri-valent. This would suggest that, for oxide systems, the B cation could be chosen from several of the transition metals, because they are of proper size and oxidation state to be accommodated in the octahedral sites. The various formal oxidation states for these metal ions would be 3+ to 5+, as demonstrated below ... 

In gas-phase chemistry it is straightforward to specify the concentrations of all of the chemical species, such as by a single array of the species mole fractions, which sums to unity. The situation can be much more complex in heterogeneous reactions. For example, there may be multiple, distinct solid phases, or different types of surfaces or materials all present simultaneously. The formalism that we describe is a very general and systematic way to account for the different groupings and normalization constraints among many col-... 

It is with the representation of chemical species by their so-called empirical formula (i.e. with no reference to structure) that we are here concerned. In such a representation ethyl alcohol is C2H60, and not C2H5OH or CH3CH2OH as more structured representations would have it. They will be referred to, where necessary, as representations of Class I. A formal theory of a simple structured representation has indeed been adumbrated [1,2], but it is not yet clear what the algebraic structure of the reaction system may be. 

The chemical properties of particles are assumed to correspond to thermodynamic relationships for pure and multicomponent materials. Surface properties may be influenced by microscopic distortions or by molecular layers. Chemical composition as a function of size is a crucial concept, as noted above. Formally the chemical composition can be written in terms of a generalized distribution function. For this case, dN is now the number of particles per unit volume of gas containing molar quantities of each chemical species in the range between ft and ft + / ,-, with i = 1, 2,..., k, where k is the total number of chemical species. Assume that the chemical composition is distributed continuously in each size range. The full size-composition probability density function is... 

If one prepares a solution of 1 mol L-1 NaCl, it is not clear whether there will be 1 mol L 1 Na+ or 1 mol L 1 Cl-, because the two ions may react with each other or with other chemical species in solution to form additional solution species with different valencies. For example, assuming that the NaCl solution contains also lead (Pb2+), Pb2+ and Cl- would react with each other to form the dissolved chemical species PbCl+, PbCl2, and so on. Chemists distinguish the two situations (free vs. paired solution species) by referring to the total dissolved concentration of an element as formality (F), and to the concentration of certain known dissolved chemical species (e.g., Na+ and Pb2+) as molarity (M) (Table 1.9). Field practitioners of environmental chemistry almost always refer to concentrations of elements because it is total dissolved concen-... 

A redox reaction implies a change in the oxidation state of atoms in one or more of the reactant(s). The most common case is when—at least in a formal sense—a chemical species (atom, ion, radical, or molecule) loses one or more electrons while another gains them. The first species increases its oxidation number (or oxidation state) and is said to be oxidized, whereas the oxidation state of the second decreases and is said to be reduced. 

Looking at this list it is obvious that the selection of a borderhne between selenium compounds which maybe considered as the derivatives having lower oxidation state and their higher oxidation state analogues is to some extent a matter of formality and, as such, may always be considered as an arbitrary choice. After analysis of a prehminary outline of the chapters in this volume and taking into account the fact that pentavalent, tetracoordinated compounds have not yet been reported and that the first organic member of the selenurane oxide family has just been isolated [4] as a stable chemical species, we have decided to discuss here the recent synthetic apphcation of selenium compounds from the classes c-f, h and j. 

The formalism of this paper can also be applied to mixtures other than those of isotopes, such as binary cation systems or liquid alloys. The treatment following Equation 4 can easily be shown for the case of different chemical species A and B, to lead to a counterpart of Equation 11, in the form... 

Each electronic state of the given stoichiometric family corresponds to a formal potential energy hypersurface E(K). Clearly, the notions of chemical species, chemical identity, and molecular deformation are dependent on the electronic state. A specific nuclear arrangement that is stable for one electronic state... 

Many minerals with which water comes into contact are oxides, hydroxides, carbonates, and hydroxide carbonates. The same ligands (hydroxides and carbonates) are dissolved constituents of all natural waters. The solid and solute chemical species under consideration belong to the ternary system Me" -H20-CO2. In connection with hydrolysis (Section 6.4) we have already dealt with solubility equilibria of (hydr)oxides. To be complete, we resume a brief formal treatment. 

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