Solubility temperature, variations with

In contrast, inverse solubility salts are less soluble as the temperature of the solution is raised. Examples of inverse solubility salts are CaCOs and CaS04. It will be readily appreciated that water containing inverse solubility salts used for cooling purposes is likely to cause fouling problems because as heat is abstracted by the water, its temperature will rise, and if it is saturated with inverse solubility salts, precipitation of the salts will occur. In Fig. 6, the sequence of events that occurs when an inverse solubility salt is heated is illustrated. The curve represents the solubility variation with temperature. The solution of the salt at point A is not saturated. As the solution represented by A is heated it will eventually reach the solubility curve at... 

FIGURE 8.22 The variation with temperature of the solubilities of six substances in water. 

Solubility variation with pressure Low-pressure solubility High-pressure solubility Heat of solution—related to variation of solubility with temperature at fixed pressure Relatively linear Low Continues to increase Relatively low and approximately constant with loading Highly nonlinear High Levels off Relatively high and decreases somewhat with increased solute loading... 

As seen in Figure 4.1, the noble gas solubility in water shows considerable variation with temperature. Therefore, noble gas contents in groundwater, which was in solubility equilibrium with the ambient, can be used to estimate the atmospheric... 

The solubility product is equal to Ca x AI(OH)4 x [OH , where curly brackets denote species activities and [OH ] may be replaced by 2[Ca ] - [A1(0H)4"]. As the concentrations are low, activity coefficients may be calculated from simplified Debye-Hiickel theory. Solubility products may thus be obtained from experimental data (NI8,B118,BI 19.C48) (Table 10.2). The variations in solubility products with temperature may be represented by empirical equations of the form... 

Estimation of gas-liquid mass-transfer rates also requires the knowledge of solubilities of absorbing and/or desorbing species and their variations with temperature (i.e., knowledge of heats of solution). In some reactions, such as hydrocracking, significant evaporation of the liquid occurs. The heat balance in a hydrocracker would thus require an estimation of the heat of vaporization of the oil as a function of temperature and pressure. The data for the solubility, heat of solution, and heat of vaporization for a given reaction system should be obtained experimentally if not available in the literature. 

Figure 1. Solubility parameter of SCF COj variation with temperature and pressure. (Reprinted with permission from Ref. 5, Fig. 2, 1984, American Chemical Society.)...

The process of fractional crystallization is a technique by which chemists separate and purify many substances. This process takes advantage of differing variations with temperature of the solubilities of several components in a given solvent. If one of the components is insoluble at all temperatures whereas other components are soluble at some temperature, the insoluble component can be separated easily by filtration. If the solubility of one of the soluble components in the mixture increases rapidly with temperature whereas the solubility of the other soluble component increases only slightly with temperature, an appropriate temperature can be chosen such that one of the components will be only slightly soluble whereas the other will be almost entirely in solution. With one component present primarily in the solid phase and the other in solution, a separation can again be achieved easily by filtration. The solvent used may dissociate components that are salts, but must not react further chemically with the components. The solvent must also allow the components to separate as well formed crystals and must be easily removed from the components, for example, by evaporation. Water serves as an appropriate solvent in this experiment. In many industrial operations mixed solvent systems must be used. 

Effect of Temperature on SolvbUity Heat of Solution The variation in solubility of a slightly soluble substance with temperatures is given by the thermodynamic relation ... 

To this point, the various possible types of solubility-limiting boundary have been discussed, but the variation of the nature of the solubility boundary with temperature has not been described. A systematic pattern does exist and is very useful to know. 

The variation of the solubility constants with temperature for bunsenite and microcrystalline theophrastite indicates that there is a crossover in stability at about 100 °C. This is marginally larger than, but still consistent with, the temperature for this transition calculated by Palmer and Gamsjager (2010) of 77"C. 

Variation in solubility of three inorganic compounds with temperature. 

There seem to be no direct calorimetric determinations of enthalpies of solution of rare-earth tribromides in nonaqueous solvents,3 and very few reports on the temperature variation of solubilities whence solution enthalpies might be roughly estimated. The most detailed set of data concerns cerium tribromide in pyridine (257). In this system there exists a series of solvates (cf. Section IH,C,2), but sufficient solubilities were determined for the estimation of enthalpies of solution of each solvate. These enthalpies are included in Fig. 3, which shows an extraordinary zig-zag variation of solubility with temperature. The actual values of enthalpies of solution cannot be accurate, but at least it is clear that they change sign and magnitude in an eccentric manner. 

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