Equilibrium solid-aqueous solution

Although nearly identical solid-aqueous solution compositions are observed in recrystallization from two directions under conditions of total constant composition, this alone is insufficient proof of the establishment of equilibrium. In order to test for equilibrium, the solid solution activity coefficients must be determined and used to compare observed solid and aqueous solution compositions with the appropriate values expected at equilibrium. 

Aagaard Helgeson 1982), provided that solution pH and temperature remain constant However, the solution saturation state is difficult to define because glass cannot be in equilibrium with aqueous solution. Accordingly, the identity of the rate-limiting solid for glass is controversial, but for the moment, we will consider the simplest of the potential candidates. 

Equilibrium reactions at the solid-aqueous solution interface may be characterized by those in which oxidation or reduction does or does not occor, A reaction without oxidation or reduction may be repreaenred by the reaction... 

It has been amply demonstrated that hydrated electrons do not exist at equilibrium in aqueous solutions (except in the presence of high energy radiation). Therefore in definitions of pe such as (18.38) the electrons are usually referred to as hypothetical and their physical state is not specified. Hostetler (1984) considers two possible physicochemical states electrons could have (even if hypothetical) in aqueous solutions (i) electrons in an inert solid Pt sample electrode (called 6(se)) and (ii) hydrated electrons existing as independent species in aqueous solution (e(a,)). He then considers each of these possibilities in detail, and concludes that neither case can be considered to be represented by the pe term in equations such as (18.38). In other words, the quantities pe (in equation 18.44), pe(SE) and pe aq) are all different quantities, pe in equation (18.44) must refer to some other completely hypothetical, unspecified state that we might call pe . Does this mean thatpe calculations are in some way physically unjustified or incorrect ... 

Assuming chemical equilibrium between aqueous solution and solid phase at constant temperature and pressure, concentration of dissolved species could be estimated. In order to estimate the concentration the values of other variables (concentration and activity coefficient of each component in solid phase and activity coefficient of dissolved species in aqueous solution) have to be estimated. 

Let us consider precipitation of (Ca, Mn)C03 solid solution from aqueous solution. It is assumed that small amounts of precipitation, dlMnCOs] and d [CaCOs], are in equilibrium with aqueous solution. This equilibrium is expressed as... 

Fig. 14 Liquid liquid equilibrium of aqueous solutions of NaPA 5 and PEG 34. Symbols experi mental equilibrium compositions [115] dotted lines experimental tie lines solid lines correlation results...

TABLE 17. Salt VAPOUR PRESSURES (mm Hg) OF SATURATED AQUEOUS SOLUTIONS IN EQUILIBRIUM WITH SOLID SALTS Temperature % Humidity 10" 15" 20" 25" 30" at 20" ... 

Table 1.7 shows typical half reactions for the oxidation of a metal M in aqueous solutions with the formation of aquo cations, solid hydroxides or aquo anions. The equilibrium potential for each half reaction can be evaluated from the chemical potentials of the species involved see Appendix 20.2) and it should be noted that there is no difference thermodynamically between equations 2(a) and 2(b) nor between 3(a) and 3(b) when account is taken of the chemical potentials of the different species involved. 

The data given in Tables 1.9 and 1.10 have been based on the assumption that metal cations are the sole species formed, but at higher pH values oxides, hydrated oxides or hydroxides may be formed, and the relevant half reactions will be of the form shown in equations 2(a) and 2(b) (Table 1.7). In these circumstances the a + will be governed by the solubility product of the solid compound and the pH of the solution. At higher pH values the solid compound may become unstable with respect to metal anions (equations 3(a) and 3(b), Table 1.7), and metals like aluminium, zinc, tin and lead, which form amphoteric oxides, corrode in alkaline solutions. It is evident, therefore, that the equilibrium between a metal and an aqueous solution is far more complex than that illustrated in Tables 1.9 and 1.10. Nevertheless, as will be discussed subsequently, a similar thermodynamic approach is possible. 

The Number of Dipoles per Unit Volume. The Entropy Change Accompanying Proton Transfers. The Equilibrium between a Solid and Its Saturated Solution. Examples of Values of L and AF°. The Change of Solubility with Temperature. Uni-divalent and Other Solutes. Lithium Carbonate in Aqueous Solution. H2COj in Aqueous Solution. Comparison between HjCOj and Li2C03 in Aqueous Solution. Heats of Solution and the Conventional Free Energies and Entropies of Solution. 

In this and succeeding chapters, a wide variety of different types of equilibria will be covered. They may involve gases, pure liquids or solids, and species in aqueous solution. It will always be true that in the expression for the equilibrium constant—... 

Equilibrium curve for silver chloride. Silver chloride (s) is in contact with Ag+ and Cl- ions in aqueous solution. The product Q of the concentration of ions [Ag+] X [Cl-] is equal to Ksp (curved line)when equilibrium exists. If 0 > K,p, AgCI(s) tends to precipitate out until equilibrium is reached. If 0 < Ksp, additional solid dissolves. 

A typical example is as follows. Benzoic acid, C6H5COOH, is a solid substance with only moderate solubility in water. The aqueous solutions conduct electric current and have the other properties of an acid listed in Section 11-2.1. We can describe this behavior with reaction (42) leading to the equilibrium relation (43) ... 

This, at first perhaps surprising fact, is important to remember as the same situation arises in solid state electrochemistry. To understand its validity it suffices to remember that the definition of the reference (zero) energy level of electrons for the she scale is simply the state of an electron at the Fermi level of any metal in equilibrium with an aqueous solution of pH=0 and pH2=l atm at 25°C. 

Abstract Inorganic polysulfide anions and the related radical anions S play an important role in the redox reactions of elemental sulfur and therefore also in the geobio chemical sulfur cycle. This chapter describes the preparation of the solid polysulfides with up to eight sulfur atoms and univalent cations, as well as their solid state structures, vibrational spectra and their behavior in aqueous and non-aqueous solutions. In addition, the highly colored and reactive radical anions S with n = 2, 3, and 6 are discussed, some of which exist in equilibrium with the corresponding diamagnetic dianions. 

This is the usual first step. We need to know our destination before we can map out a route. We are asked for the value of the equilibrium constant for a solid dissolving to form an aqueous solution. 

The color of an aqueous solution of copper(II) chloride shows that copper(II) cations are present in the aqueous phase at equilibrium with the solid salt. 

C16-0100. A student mixes sodium chloride and water until the solid and the aqueous solution are at equilibrium. If more solid sodium chloride is added to this mixture, does the concentration of sodium chloride in the aqueous solution change Explain your answer in molecular terms. 

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