Activity equilibria

Eq. 3 is the function developed by Henry Eyring to describe equilibrium activation free energy relationships [141 ]. 

In this example of the corrosion of zinc in a reducing acid of pH = 4, the corrosion product is Zn (aq.), but at higher pHs the thermodynamically stable phase will be Zn(OH)j and the equilibrium activity of Zn will be governed by the solubility product of Zn(OH)j and the pH of the solution at still higher pHs ZnOj-anions will become the stable phase and both Zn and Zn(OH)2 will become unstable. However, a similar thermodynamic approach may be adopted to that shown in this example. 

Pourbaix has evaluated all possible equilibria between a metal M and HjO (see Table 1.7) and has consolidated the data into a single potential-pH diagram, which provides a pictorial summary of the anions and cations (nature and activity) and solid oxides (hydroxides, hydrated oxides and oxides) that are at equilibrium at any given pH and potential a similar approach has been adopted for certain M-H2O-X systems where A" is a non-metal, e.g. Cr, CN , CO, SOj , POj", etc. at a defined concentration. These diagrams give the activities of the metal cations and anions at any specified E and pH, and in order to define corrosion in terms of an equilibrium activity, Pourbaix has selected the arbitrary value of 10 ° g ion/1, i.e. corrosion of a metal is defined in terms of the pH and potential that give an equilibrium activity of metal cations or anions > 10 g ion/1 conversely, passivity and immunity are defined in terms of an equilibrium activity of < 10 g ion/1. (Note that g ion/1 is used here because this is the unit used by Pourbaix in the S.I, the relative activity is dimensionless.)... 

Finally, it should be noted that although the arbitrary activity of 10 g ion/1 represents a very low concentration of metal ions it could be significant in certain circumstances, e.g. lead at that concentration would render potable water toxic. It should also be noted that if the equilibrium is continuously disturbed, e.g. by a flowing solution, significant amounts of metal will corrode even at an equilibrium activity of 10 g ion/1. 

At equilibrium, the cell would be able to do no useful work, and its emf must then be zero. For equilibrium activities of the variable reagents of the summed up equation shown... 

LIQUID-LIQUID EQUILIBRIUM ACTIVITY COEFFICIENT MODELS... 

Ka is known as the equilibrium constant. It represents the equilibrium activities for a system under standard conditions and is a constant at constant temperature. 

As a final example, we balance the reaction between the zeolite calcium clinop-tilolite and the mica prehnite [Ca2Al2Si30io(OH)2] in the presence of quartz, and calculate at 200 °C the equilibrium activity ratio aC d i i /a, . The commands... 

As before, the saturation ratio S can also be expressed as a/ao, where a and a0 are the actual and equilibrium activities, respectively, of the solutes that characterize the solubility. Once nuclei of critical size Xj+1 (in Eq. 6.1) have been formed, crystallization is spontaneous. 

In writing the Etudes de dynamique chimique (1884), van t Hoff drew on Helmholtz s 1882 paper but especially on the work of August Horstmann, a student of Bunsen, Clausius, and H. Landolt.59 As has often been discussed, van t Hoffs was an ambitious and original synthesis of disconnected ideas and theories about opposing forces, equilibrium, active masses, work and affinity, electromotive force, and osmotic pressure. He demonstrated that the heat of reaction is not a direct measure of affinity but that the so-called work of affinity may be calculated from vapor pressures (the affinity of a salt for its water of crystallization), osmotic pressure (affinity of a solute for a solution), or electrical work in a reversible galvanic cell (which he showed to be proportional to the electromotive force). 

During the period 1940-1962, the cracking catalysts used most widely commercially were the aforementioned acid-leached clays and silica-alumina. The latter was made in two versions low alumina (about 13% AI2O3) and high alumina (about 25% AI2O3) contents. High-alumina-content catalysts showed a higher equilibrium activity level and surface area. 

The most important applications of Cu ISEs are in the direct determination of Cu " in water [169, 372,410], complexometric titration of various metal ions using Cu " as an indicator [30, 143,269, 385] and complexometric titrations of Cu " [409]. This ISE has also been used in the determination of the equilibrium activity of Cu in various Cu complexes in order to determine the stability constants (see [46, 285, 317, 318,427, 445]), in the determination of the solubility of poorly soluble salts [122] and in the determination of the standard Gibbs transfer energies [58]. It can also be used in concentrated electrolytes [170]. 

The activities of solute species in an aqueous solution in equilibrium with K-feldspar at the P and T of interest will be those dictated by equation 8.232. Let us now imagine altering the chemistry of the aqueous solution in such a way that the activities of the aqueous species of interest differ from equilibrium activities. New activity product Q ... 

Prior to evaluation in the pilot plant, all catalysts were steam treated to simulate equilibrium activity. 

Furthermore, the equilibrium constant is also related to the equilibrium activities of the species involved. For convenience, the activities are often replaced by concentrations to yield the more practical expression... 

Make an estimate of the equilibrium activity per liter of cooling water due to 16N in a reactor that has an internal flux of 1013 neutrons/cm 2-s. 

Recall that the equilibrium activity, also called the saturation activity, occurs when the rate of production is equal to the rate of decay and requires that the sample be irradiated for more than three half-lives, or 22 s for 16N. Also, 1 mb am is 1 x 10 27cm2, thus,... 

The equilibrium constant, K, has the same form as Q, the reaction quotient, except that it uses the equilibrium activities. The equilibrium constant is related to the standard reaction free energy by Eq. 10, AGr° = -RTlnK. 

Use the Chemical Equilibrium activity (eChapter 13.1) to explore the reaction between the iron(III) ion and the thiocyanate ion. 

C vapor-liquid equilibrium-activity coefficient, measured range 20-50°C, Cooling et al. 1992)... 

Bowers T.S., Jackson K.J., and Helgeson H.C. (1984) Equilibrium Activity Diagrams (for Coexisting Minerals and Aqueous Solutions at Pressures and Temperatures of 5 KB and 600°C). Springer-Verlag, Berlin, 397 pp. 

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