Solution-vapour equilibrium

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" ... 

We shall now assume that it is possible to have a system in equilibrium composed of the various phases at a specified temperature and total pressure. This will be characterised by certain definite relations between the compositions of the phases (for example, a solid salt, saturated solution, vapour of the solvent). Let 77, T = total pressure, and temperature, of the system. n = number of components (cf. 84). r = phases ... 

The vapour fraction of the solute is moved down the column by the carrier gas and the equilibrium between the two phases is destroyed. However, in an attempt to re-establish an equilibrium, solute molecules leave the liquid phase restoring the partial pressure above the solution. The solute vapour which has been moved down the column encounters fresh solvent and a new equilibrium is established. 

VAPOUR PRESSURES (mm Hg) OF SATURATED AQUEOUS SOLUTIONS IN EQUILIBRIUM WITH SOLID SALTS... 

The (liquid 4- liquid) equilibria diagram for (cyclohexane + methanol) was taken from D. C. Jones and S. Amstell, The Critical Solution Temperature of the System Methyl Alcohol-Cyclohexane as a Means of Detecting and Estimating Water in Methyl Alcohol , J. Chem. Soc., 1930, 1316-1323 (1930). The G results were calculated from the (vapor 4- liquid) results of K. Strubl, V. Svoboda, R. Holub, and J. Pick, Liquid-Vapour Equilibrium. XIV. Isothermal Equilibrium and Calculation of Excess Functions in the Systems Methanol -Cyclohexane and Cyclohexane-Propanol , Collect. Czech. Chem. Commun., 35, 3004-3019 (1970). The results are from M. Dai and J.-P.Chao, Studies on Thermodynamic Properties of Binary Systems Containing Alcohols. II. Excess Enthalpies of C to C5 Normal Alcohols + 1,4-Dioxane , Fluid Phase Equilib., 23, 321-326 (1985). 

Concomitant crystallization is by no means limited to crystallization from solution, nor to preservation of constant molecular conformation. As noted in Section 2.2.5 the classic pressure vs temperature phase diagram for two solid phases (Fig. 2.6) of one material exhibits two lines corresponding to the solid/vapour equilibrium for each of two polymorphs. At any one temperature one would expect the two polymorphs to have different vapour pressures. This, in fact, is the basis for purification of solids by sublimation. Nevertheless there are examples where the two have nearly equal vapour pressures at a particular temperature and thus cosublime. This could be near the transition temperature or simply because the two curves are similar over a large range of temperatures or in close proximity at the temperature at which the sublimation is carried out. For instance, the compounds 3-VI and 3-Vn both yield two phases upon... 

Finally, in the solvated electron solution/vapour system electronic emission can occur in the equilibrium manner, i.e., as thermoionic emission... 

Table 1 summarizes the basic relationships that link energy characteristics of excess electrons with the values measured by the aforementioned methods (see also Fig. 1). In the equations given therein, i.e. in Eqs. (5) and (6) w , w , and w denote respectively metal-to-vacuum, metal-to-solution, and solution-to-vacuum photoemission work functions AT is the Volta potential difference for a metal-solution system Eg is the equilibrium potential of the electrode in solvated electron solution and il(RE) is the Fermi level of the reference electrode. Equation (6) is approximate (see above) because the solvated electron entropy has not been taken into consideration. The main error in equating the heat of electron solvation and the activation energy of the thermoemission current for the solvated electron solution is caused by the variation in the solution s surface potential with temperature apparently, here specific adsorption of solvated electrons (or of an alkali metal) on the solution/vapour interface makes major contribution to the surface potential . This error can be probably neglected if measurements are taken in very dilute solutions (<10 mol/1, see ) of the alkali metal. This follows from the dependence measured in between thermoemission current and the concentration of sodium in hexamethylphosphotriamide. 

Corresponding to the point Q/the melting-point of pure iodine, there is the point C, which represents the vapour pressure of iodine at its melting-point. At this point three curves cut i, the sublimation curve of iodine 2, the vaporisation curve of fused iodine 3, CiB, the vapour-pressure curve of the saturated solutions in equilibrium with solid iodine. Starting, therefore, with the system solid iodine— liquid iodine, addition of chlorine will cause the temperature of equilibrium to fall continuously, while the vapour pressure will first increase, pass through a maximum and then fall continuously until the eutectic point, B (Bjl), is reached. At this point the system is invariant, and the pressure will therefore remain constant until all the iodine has disappeared. As the concentration of the chlorine increases in the manner represented by the curve B/H, the pressure of the vapour also increases as represented by the curve Bj/iHi. At the eutectic point for iodine monochloride and iodine trichloride, the pressure again remains constant until all the monochloridc has disappeared. As the concentration of the solution passes along the curve HF, the pressure... 

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