JOINT EXPERT SPECIATION SYSTEM

JESS - JOINT EXPERT SPECIATION SYSTEM

Chemical reactions are described using species symbols. They can be written in any form just as long as the principles of conservation of mass and charge are obeyed. In other words, the JTH database does not impose constraints on which species are formulated as reactants and which as products.

Reactions are represented in much the same way as they are in ordinary chemical writing, i.e. the symbols of the reactant species appear on the left hand side of an equals sign, =, and the symbols of the products appear on the right hand side. Species on the same side of the equation are usually separated from one another by plus signs, +, but minus is also acceptable, if that happens to be appropriate. Note that in the representation of a chemical equation as just described, the signs =, +, - must always be surrounded by blank spaces. This permits the database programs to distinguish the species occurring in the reaction and not to be confused by the signs (of electronic charge) which occur in species' symbols.

Consider the JESS format for reactions used in the following examples.

H+1 + OH-1 = H2O

Cu+2 + 2<OH-1> = Cu+2_OH-1(2)

Here, H+1, OH-1, H2O and Cu+2 are primitive symbols and Cu+2_OH-1(2) is a composite symbol.

Phase designators such as (s) or (g) are employed in parentheses for all species other than aqueous ones. These may be part of a primitive species symbol, as in Cu(s) or H2(g), or part of a composite species symbol, as in Cu+2_OH-1(2)_(s).

Some other rules for representing reactions are (a) that species may be enclosed in angle brackets, < >, if they are preceded by a coefficient; (b) coefficients can be real or integer; and (c) water must be included if needed achieve complete mass-balance. Another example would thus be as follows.

Fe+3 + 3<OH-1> = FeOOH(alpha,s) + H2O

Clearly, this way of specifying reactions requires a lot of care and entering many reactions like this would be tedious. Unlike the species symbols, the representation of reactions cannot be truncated. Fortunately there are other ways of doing things so you will rarely need to construct these specifications in full.