Potential of water

Extended stabiUty testing is a necessity for emulsion systems in metal containers because of the corrosion potential of water. In most cases where a stable emulsion exists, there is less corrosion potential in a w/o system because the water is the internal phase. 

In a state of equilibrium the chemical potentials of water and water vapor are equal ... 

The Ag/AgCl, Cl" electrode is probably the best reference electrode for measuring potentials of waters at elevated temperatures. 

The swelling pressure or osmotic deswelling data can be, therefore, described as the functions of n(w) by either of the theories [115]. This description can be then applied to determining the network parameters (see, for example, Ref. [22]). On the other hand, the swelling pressure which is directly connected with the chemical potential of water in the gel ... 

Younis, H.M., Boyer, J.S. Govindjee (1979). Conformation and activity ofchloro-plast coupling factor exposed to low chemical potential of water in cells. Biochimica et Biophysica Acta, 548, 328-40. 

Preparation of an uncontaminated surface of an aqueous solution is very difficult. Even minute traces of adsorbable organic impurities strongly influence the surface potential of water. Cleaning of the aqueous surface (e.g., by siphoning off the surface layer) is usually necessary, while for organic solutions it is usually not needed. ... 

Adsorption of a dipolar substance at the w/a and w/o interfaces changes surface tension and modifies the surface potential of water (Fig. 11). As seen in Fig. 11, the change in compensation voltage due to adsorption is the surface potential difference, usually called the surface potential or better the adsorption potential and often indicated unnecessarily by AV. ... 

Figure 11. Influence of the adsorbed molecules B on the surface potential of water.

The presence of adsorbed Langmuir monolayers may induce very high changes in the surface potential of water. For example, A% shifts attaining ca. -0.9 (hexadecylamine hydrochloride) and ca. + 1.0 V (per-fluorodecanoic acid) have been observed. " ... 

The surface potential of water, x , as any other surface potential, is not measurable. Its probable value is inferred from indirect observations. Such a potential difference has been postulated because the tetrahedral charge... 

The impossibility of x being equal to about 1 V, as suggested by Kamieifki, " " has been demonstrated by Frumkin on the basis of a discussion of the real energies of hydration. Estimates from the variation in the solution surface potential with electrolyte molarity have yielded the value of +0.025 0.010 V.21 For methanol, the same method results in a value of -0.09 V.146 Later the authors of that investigation stated that both estimated values should be understood as the lower limits of surface potentials of water and methanol. "... 

Recent molecular dynamics studies of properties of the water surface have led to predictions of the surface potential of water that differ not only in magnitude but also in sign. The main problem is connected with the difficulty of proper definition of the surface potential of a real polar... 

Figure 12. Difference between the surface potentials of water and an organic solvent.

This approach allowed us also to determine the difference in the surface potentials between mutually saturated water and an organic solvent namely, nitrobenzene, nitroethane and 1,2-dichloroethane, and isobutyl methyl ketone (IBMK). The qualitative data show a very strong influence of the added organic solvent on the surface potential of water, while the presence of water in the nonaqueous phase has practically no... 

The surface potential of a solution can be calculated, according to Eq. (10.18), from the dilference between the experimental real energy of solvation of one of the ions and the chemical energy of solvation of the same ion calculated from the theory of ion-dipole interaction. Such calculations lead to a value of -1-0.13 V for the surface potential of water. The positive sign indicates that in the surface layer, the water molecules are oriented with their negative ends away from the bulk. 

Stresses caused by chemical forces, such as hydration stress, can have a considerable influence on the stability of a wellbore [364]. When the total pressure and the chemical potential of water increase, water is absorbed into the clay platelets, which results either in the platelets moving farther apart (swelling) if they are free to move or in generation of hydrational stress if swelling is constrained [1715]. Hydrational stress results in an increase in pore pressure and a subsequent reduction in effective mud support, which leads to a less stable wellbore condition. 

Growth experiments were conducted using bacteria from oil installations with several chemicals normally used in injection water treatment. The studies revealed that some chemicals could be utilized as nitrogen sources, as phosphorus sources, and as carbon sources for the bacteria [1696]. Therefore it is concluded that the growth potential of water treatment additives may be... 

Replacement of gas by the nonpolar, e.g., hydrocarbon phase (or oil phase) is used to modify the interactions between molecules in a spread film of investigated long-chain substances [6,15,17,18]. The nonpolar solvent-water interface possesses the advantage over that between gas and water, that the cohesion (i.e., interactions between adsorbed molecules due to dipole and van der Waals forces) is negligible. Thus, at the oil-water interfaces behavior of adsorbates is much closer to ideal, but quantitative interpretation may be uncertain, in particular for the higher chains which are predominantly dissolved in the oil phase to an unknown activity. Adsorption of dipolar substances at the w/a and w/o interfaces changes surface tension and modifies the surface potential of water [15] ... 

The physical meaning of the g" (ion) potential depends on the accepted model of ionic double layer. The proposed models correspond to the Gouy Chapman diffuse layer, with or without allowance for the Stern modification and/or the penetration of small counterions above the plane of the ionic heads of the adsorbed large ions [17,18]. The presence of adsorbed Langmuir monolayers may induce very high changes of the surface potential of water. For example. A/" shifts attaining ca. —0.9 (hexadecylamine hydrochloride), and ca. -bl.OV (perfluorodecanoic acid) have been observed [68]. 

Firstly, the analysis implicitly allows water reuse even in a situation where the source and sink processes are simultaneously active as observed in Fig. 12.6. According to Fig. 12.6, in concentration interval (20CMKX) ppm), 37.5 t and 25 t of water are available for reuse in the (0.5-1.0 h) and (1.0-1.5 h) time intervals, respectively. This semi-batch behaviour is further observed in the water network shown in Fig. 12.7. Some of the water from process 3 is reused in process 1, even though process 1 is 0.5 h from completion. This would not be possible for truly batch operations, since the reuse potential of water could only be realized after the completion, and not during the course of the process. 

It should be realized that by increasing the reuse potential of water in this system of operations, the target water demand has decreased from 1560 to 1000 kg. It also transpired during the analysis that the value of x could be reduced to zero without increasing the overall targets for the subsequent cycles, since B and C washes do not pick up any salt, and the water could therefore be used in the A wash of the... 

A quasichemical theory, using ab initio simulation (rPBE functional) to generate data for the computation of the various contributions to the free energy, yields an estimate for the excess chemical potential of water very close to the experimental value. 

The most fundamental manner of demonstrating the relationship between sorbed water vapor and a solid is the water sorption-desorption isotherm. The water sorption-desorption isotherm describes the relationship between the equilibrium amount of water vapor sorbed to a solid (usually expressed as amount per unit mass or per unit surface area of solid) and the thermodynamic quantity, water activity (aw), at constant temperature and pressure. At equilibrium the chemical potential of water sorbed to the solid must equal the chemical potential of water in the vapor phase. Water activity in the vapor phase is related to chemical potential by... 

Reaction (1) is a reversible process, and it can be a source of superoxide if only its equilibrium is shifted to the right. The estimation of the equilibrium constant for this reaction in aqueous solution is impossible because the reduction potential of water-insoluble ubiquinone in water is of course undetectable. However, Reaction (1) occurs in the mitochondrial membrane and therefore, the data for the aqueous solutions are irrelevant for the measurement of its equilibrium. Some time back we studied Reaction (1) in aprotic media and found out that Ki is about 0.4 [23]. As the ubiquinone concentration in mitochondria is very high (it is about... 

The concept of substance activity was derived by Gilbert N. Lewis in 1907 from the laws of equilibrium thermodynamics and is described in detail in the text entitled Thermodynamics and the Free Energy of Chemical Substances by Lewis and Randell (1923). In a homogeneous mixture, each component has a chemical potential (jjl), which describes how much the free energy changes per mole of substance added to the system. The chemical potential of water (pw) in a solution is given by... 

---