Thermodynamic driving force dissolution

As with the calcareous tests, BSi dissolution rates depend on (1) the susceptibility of a particular shell type to dissolution and (2) the degree to which a water mass is undersaturated with respect to opaline silica. Susceptibility to dissolution is related to chemical and physical factors. For example, various trace metals lower the solubility of BSi. (See Table 11.6 for the trace metal composition of siliceous shells.) From the physical perspective, denser shells sink fester. They also tend to have thicker walls and lower surface-area-to-volume ratios, all of which contribute to slower dissolution rates. As with calcivun carbonate, the degree of saturation of seawater with respect to BSi decreases with depth. The greater the thermodynamic driving force for dissolution, the fester the dissolution rate. As shown in Table 16.1, vertical and horizontal segregation of DSi does not significantly coimter the effect of pressure in increasing the saturation concentration DSi. Thus, unlike calcite, there is no deep water that is more thermodynamically favorable for BSi preservation they are all corrosive to BSi. 

Phase dissolution in polymer blends. The reverse process of phase separation is phase dissolution. Without loss of general validity, one may assume again that blends display LCST behavior. The primary objective is to study the kinetics of isothermal phase dissolution of phase-separated structures after a rapid temperature-jump from the two-phase region into the one-phase region below the lower critical solution temperature. Hence, phase-separated structures are dissolved by a continuous descent of the thermodynamic driving force responsible for the phase separation. The theory of phase separation may also be used to discuss the dynamics of phase dissolution. However, unlike the case of phase separation, the linearized theory now describes the late stage of phase dissolution where concentration gradients are sufficiently small. In the context of the Cahn theory, it follows for the decay rate R(q) of Eq. (29) [74]... 

In Fig. 1 the super saturation range is located below the equilibrium curve corresponding to the equality fis,oo = fie,oo- In the case when ps < / c>00, the difference Ps Pc,oo <0 defines the electrochemical undersaturation, which, if applied, would cause the electrochemical dissolution of the bulk liquid or crystalline new phase. Thus, the quantity Ap defines the thermodynamic driving force of the two opposite types of electrochemical first-order -+ phase transition and it is of fundamental importance to express it by means of physical quantities, which can be easily measured and controlled. 

Initially, crystallite growth occurs rapidly either by ion dissolution/reprecipitation (Ostwald ripening) or by surface atom diffusion, due to the requirement for lowering the surface energy of any individual crystallite. This thermodynamic driving force will tend to eliminate the incomplete faces but with the drive to lower the surface energy, the crystallites also will strive towards sphericity. This means, that to all intents and purposes, the ratios ofthe (111) and (100) faces should be approximately the same. Bett et al.1 noted that as the platinum crystallite sizes grew, the size distribution increased. If this is so, then... 

In a saturated solution, including one saturated with respect to protein, two states exist in equilibrium the solid phase and one consisting of molecules free in solution. At saturation, no net increase in the proportion of solid phase can accrue, since it would be counterbalanced by an equivalent dissolution. Thus crystals do not grow from a saturated solution. The system must be in a nonequilibrium, or supersaturated state to provide the thermodynamic driving force for crystallization. 

Because of the pH-dependent solubility of (hydr)oxides, the thermodynamic driving force of reductive dissolution increases with decreasing pH. Thus, the rate constant of reductive dissolution may follow the same trend. 

Last but not least, the pH dependence of the thermodynamic driving force may account for the pH dependence of the observed rate constant. Reductive dissolution of lepidocrocite with oxalate as the reductant is an ex-... 

The thermodynamic driving force for dissolution is therefore the heat of solution of the substance. For a crystalline solid, this represents the difference... 

At this point the dissolution rate of Zn is equal to that of hydrogen ions production. The corresponding current density icorr is called corrosion current of zinc in hydrochloric acid. Therefore, on the contact surface zinc-acidic solution microscopic galvanic cells are formed of the type shown in Fig. 13.3 in which the electrons made available by zinc that oxidizes reduce the acid determining a new equilibrium point in which anode and cathode have the same potential Econ The variation of the electrode potentials with respect to their equilibrium values that leads to the common value E orr is called polarization. The thermodynamic driving force that sustains corrosion is given by the difference... 

The concentration gradient across the intestinal mucosa, being the driving force for passive absorption, is affected by the thermodynamic solubility and dissolution rate of the drug in the intestinal fluids as described earlier. 

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