Vapor-solid equilibrium

The equilibrium pressure when (solid + vapor) equilibrium occurs is known as the sublimation pressure, (The sublimation temperature is the temperature at which the vapor pressure of the solid equals the pressure of the atmosphere.) A norma) sublimation temperature is the temperature at which the sublimation pressure equals one atmosphere (0.101325 MPa). Two solid phases can be in equilibrium at a transition temperature (solid + solid) equilibrium, and (liquid + liquid) equilibrium occurs when two liquids are mixed that are not miscible and separate into two phases. Again, "normal" refers to the condition of one atmosphere (0.101325 MPa) pressure. Thus, the normal transition temperature is the transition temperature when the pressure is one atmosphere (0.101325 MPa) and at the normal (liquid + liquid) solubility condition, the composition of the liquid phases are those that are in equilibrium at an external pressure of one atmosphere (0.101325 MPa). 

Equivalent expressions can be obtained for the (solid + vapor) equilibrium to give the vapor pressure of a solid, by substituting the sublimation enthalpy, AjubT/m, for Avap//m ... 

Historically, an ideal solution was defined in terms of a liquid-vapor or solid-vapor equilibrium in which each component in the vapor phase obeys Raoult s law. 

Solid-Vapor Equilibrium. In a very similar way as for the liquid-vapor equilibrium, we can derive a relationship for the temperature dependence of the vapor pressure of the solid compound. By analogy to Eq. 4-5, we write ... 

When a solution freezes, the solid is usually pure solvent. Thus the solid-vapor equilibrium (sublimation) P-T curve is unaffected by the presence of solute. The intersection of this curve and the liquid-vapor curve is the triple point (nearly the same temperature as the freezing point, which is measured at atmospheric pressure). Since a solute lowers the solvent vapor pressure, the triple point is shifted to lower temperature, as shown in Figure 11-2. Detailed calculations show that the decrease in freezing point for a dilute solution is proportional to the total molal concentration of solutes... 

Equation (1.160) is also valid for a solid-vapor equilibrium. Assuming that the latent heat of vaporization remains constant between small temperature intervals of AT, then integration of Eq. (1.160) yields... 

Temperature Liquid/vapor equilibrium Solid/vapor equilibrium ... 

At temperatnres below its triple point, a pure solid can vaporize. Solid/vapor equilibrium for a pure species is represented on a PT diagram by the subhmation curve (see Fig. 3.1) here, as for VLE, the eqnilibrinm pressure for a particnlar temperature is called the (solid/vapor) saturation pressure P... 

Solubilitiesattemperaturesand pressures above the critical values of the solvent liave important applications for supercritical separation processes. Examples are extraction of caffeine from coffee beans and separation of asplraltenes from heavy petroleum fractions. For a typical solid/vapor equilibrium (SVE) problem, tire solid/vapor saturation pressure P is very small, and the saturated vapor is for practical purposes an ideal gas. Hence 0 for pure solute vapor at this pressure is close to unity. Moreover, exceptfor very low values of the system pressure P, the solid solubility yj is small, and can be approximated by j, the vapor-phase fugacity coefficient of the solute at infinite dilution. Finally, since is very small, the pressure difference P — in the Poyntingfactor is nearly equal to P at any pressure where tins factor... 

In the forward process, called sublimation, iodine molecules change directly from the solid phase to the gas phase. In the reverse process, gaseous iodine molecules return to the solid phase. A solid-vapor equilibrium is established in each flask. 

Somorjai, G. A., Vapor pressure and solid-vapor equilibrium of CdSe (Cadmium Selenide), J. Phys. Chem., 65, (1961), 1059-1061. Cited on pages 269, 270, 464. 

A solid substance in equilibrium with its vapor phase will exhibit a well-defined vapor pressure for a given temperature, which will be independent of the relative amounts of solid and vapor present. The curve representing the solid/vapor equilibrium conditions is termed a sublimation curve, which generally takes a form similar to that of a vaporization curve. Although the sublimation pressure of a solid is often exceedingly small, for many substances it can be considerable. 

SOLID-VAPOR EQUILIBRIUM OF THE CARBON DIOXIDE-NITROGEN SYSTEM AT PRESSURES TO 200 ATMOSPHERES... 

Solid—Vapor Equilibrium of the Carbon Dioxide—Nitrogen System... 

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