Hydroxides heterogeneous equilibria

The equilibrium constants for heterogeneous reactions are also given by the general expression in Eq. 2 all we have to remember is that the activity of a pure solid or liquid is 1. For instance, for the calcium hydroxide equilibrium (reaction H),... 

By the method used on p. 416 for pure gas reactions, Nernst has shown that the integration constant can again be expressed as the sum of the vapour pressure constants of the individual volatile reacting substances. In most of the more important heterogeneous reactions only a single gas takes part in the reaction, as, for example, in the dissociation of carbonates, hydroxides, ammoniates, salt hydrates, and, further, in reactions between metals and oxygen or the halogens. In these cases the condition for equilibrium simplifies to... 

Schindler, P. W. (1967) Heterogeneous Equilibria Involving Oxides, Hydroxides, Carbonates and Hydroxide Carbonates. In Equilibrium Concepts in Natural Water Systems, Adv. Chem. Ser., No. 67, American Chemical Society, Washington DC, p. 196. 

The tendency of Pu(IV) to hydrolyze and to form real solutions, colloid solutions, or insoluble preeipitates has been known sinee the Manhattan Projeet. The main results of the earlier work in this field were summarized by Seaborg and Katz [19]. Sinee then, studies have been performed to examine in detail the equilibrium of Pu(fV) hydrolytie reaetions in different media [20,21]. Great attention has also foeused on the preparation, strueture and properties of Pu(IV) polymers or colloids [22-27]. These eompounds have found an important application in sol-gel teehnology for the preparation of nuclear fuel materials [28]. However, studies of the properties and behavior of solid Pu(IV) hydroxide in complex heterogeneous systems are rather rare. A most important result of these studies was the eonelusion that Pu(fV) hydroxide, after some aging, consists of very small Pu02 erystallites and, therefore, should be considered as a Pu(IV) hydrous oxide [23,24]. 

We shall not refer here to the application of suitable mathematical examples to this equilibrium process, as these are dealt with in detail in textbooks of physical chemistry. The ester, which is present in the upper phase of the heterogeneous system formed, is hydrophobic and readily dissolves plastics, fats, resins and other high molecular mass organic substances. The process in which it is formed is reversed when it is treated with sodium hydroxide. 

ScHiNDi.KR, P. W. 1967, Heterogeneous equilibria involving oxides, hydroxides, carbonates, and hydroxide carbonates, In Equilibrium concepts in natural water sy.stems. Am. Chem. Soc. Adv. Chem. Ser. 67, pp. 196 221. Washington, DC Am. Chem. Soc. 

The last step in complexity that we will explore in detail for the construction of diagrams to illustrate redox equilibria involves the addition of heterogeneous equilibria to redox and acid-base equilibrium diagrams. We will illustrate this system with a ps-pH diagram for iron species in aqueous solution containing no anions other than hydroxide, We will expand on this diagram later in this chapter during the discussion of iron chemistry. 

Mesmer [57] have exhaustively surveyed the literature and have evaluated heterogeneous equilibria for lanthanide and actinide hydroxides and hydrated oxides. The thermodynamic activity products (recommended by this author) to calculate free energies and ), in basic solution are listed in Table 17.3. In general, the values selected by Baes and Mesmer have been adopted however, in some cases more recent results have been selected or averaged [53,60]. These more recent results yield a monotonic relation between Ln(OH)j unit-cell volumes and K. For tetravalent ions, no hydroxides have been characterized and we assume that the dioxides are in equilibrium with hydrated dioxides, if any exist. Hence K values refer to reactions such as the following (see [361]) ... 

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