The General Case, Definitions

It is straightforward to generalise equations (3.13) and (3.14) to allow for the formation of species of any complexity from any number of components. Discussion here is limited to species formed by only three components X, Y, and Z. The generalisation to 4, 5 or any number of components is self-evident. 

The definition of equilibrium constants for such general cases is most conveniently done via the so-called formation constants fixyz, which are defined in the following way  

At this stage, we need to introduce the nomenclature used in the equilibrium literature. While there is no official agreement, the following expressions are well established and more importantly, they allow a reasonably consistent and systematic description of equilibria of any complexity. 

Components are the most basic units (molecules or ions or atoms) that interact with each other. In the above example X, Y, and Z are components. All the resulting products of the interactions (molecules or ions or complexes) are called species. In the example, one of potentially many species is XxYyZz. To be consistent and to allow elegant and efficient notation and computer coding, the components themselves are also species. Their equilibrium constant is one. The equilibrium constants fixyz as defined in (3.22) are called formation constants. The composition of a particular species is defined by a set of three stoichiometric constants written as the indices x, y, and z. If a species is composed of only two components, the appropriate index is zero. 

we need to recall a bit of basic physical chemistry. The law of mass action, as defined in equation (3.22) is not entirely correct. Instead of concentrations we ought to use the activities of all species. Formally, this is not a problem as there is a simple relationship between activity and concentration  

---

The CDC has not published a specific case definition for intoxication by urticants. However, the general case definition for vesicants states "A case in which a vesicant is detected in biologic samples. The case can be confirmed if laboratory testing is not performed because either a predominant amount of clinical and nonspecific laboratory evidence is present or an absolute certainty of the etiology of the agent is known."... 

---