Vapor pressure, pure liquid

Pure CIF3O2 is colorless as a gas or liquid and white as a solid. Some of its measured (68) physical properties are summarized in Table XX. Near its melting point the vapor pressure above liquid CIF3O2 was found to be reproducibly lower than expected from the vapor pressure curve given in Table XX. This indicates that close to the melting point some ordering effect occurs in the liquid. 

The isothermal vaporization of pure liquid i represents its transition from saturated liquid to saturated vapor at temperature T and at saturation vapor pressure P8 6. The treatment of this transition is facilitated through use of property changes of vaporization defined by equation 139 ... 

However, if activity coefficient data were calculated for component A using the pure component vapor pressure and liquid composition data on a salt free basis, the activity coefficient values would not normalize (i.e., approach unity as X approaches unity) unless the salt were insoluble in component A. A better liquid composition expression would be... 

The EOS based on the lattice fluid model has also be used to describe thermodynamic properties such as pVT behaviors, vapor pressures and liquid volumes, VLE and LLE of pure normal fluids, polymers and ionic... 

To estimate the pure component parameters, we used the technique of Panagiotopoulos and Kumar (11). The technique provides parameters that exactly reproduce the vapor pressure and liquid density of a subcritical component. Table II presents the pure component parameters that were used. For the supercritical components, the usual acentric factor correlation was utilized. 

Other Thermometric Devices. The vapor pressure of a pure liquid or solid is a physical property sensitive to temperature and thus suitable for use as a thermometer. The use of a liquid-nitrogen vapor-pressure thermometer is suggested for the range 64 to 78 K in Exp. 47. At very low temperatures (1 to 4.2 K), the vapor pressure of liquid helium can be used. 

In either case the relative distributions between the separable liquid and vapor phases are predicted from the pure component vapor pressures Pi°, liquid phase activity coefficients, y/s, and imperfection-pressure coefficients Oi s. Using these three quantities, the relative distribution is expressed as... 

Consider a single, pure fluid at constant temperature, in a cylinder fitted with a friotionless piston. If a pressure is applied on the piston which is greater than the vapor pressure of the liquid, the system will consist entirely of liquid when equilibrium is reached. No vapor will be present since at pressures greater than the vapor pressure it condenses into liquid. If, on the other hand, the pressure applied on the piston is less than the vapor pressure of the liquid only vapor will be present at equilibrium. If both liquid and vapor are present in equilibrium with one another, the pressure must be exactly equal to the vapor pressure. Pure substances behave in this manner and liquid and vapor can coexist at a given temperature only at a pressure equal to the vapor pressure. The relative amounts of liquid and vapor that coexist is determined by the volume of the system, and can vary an3nvliere from an infinitesimal amount of liquid to an infinitesimal amount of vapor. 

For biomaterials that are thermally unstable and decompose before reaching the critical temperature, several estimation techniques are available. We have used the Lydersen group contributions method ( ). Other techniques available for predicting critical properties have been reviewed and evaluated by Spencer and Daubert ( ) and Brunner and Hederer Qfi). It is also possible to determine the EOS parameters from readily measurable data such as vapor pressure, and liquid molar volume instead of critical properties (11). We used the Lydersen method to get pure component parameters because the vapor compositions we obtained were in closer agreement with experiment than those we got from pure component parameters derived by Brunner s method. The critical properties we used for the systems we studied are summarized in Table II. 

From Equations 1 and 2, the phase equilibria depend upon knowing the pure component vapor pressures P4°, liquid phase activity coefficients y and imperfection-pressure coefficients 04. The computer program which has been developed uses any of four different vapor pressure equations for providing P40. It uses the modified van Laar Equations (5) to give liquid phase activity coefficients and a Modified van der Waals Equation of State 4,6) to give imperfection-pressure coefficients 0. ... 

Figure 2.12 is the classic pressure-temperature (FT) representation of the phase changes of a pure component. There are three primary phases of pure components solid liquid, and vapor solid-solid transitions, liquid crystal phases, and so on, are also possible but will not be considered here. The solid lines represent the sublimation curve (solid —> vapor), the vapor pressure curve (liquid —> vapor) and the melting curve (solid liquid) of the pure component. The triangle represents the triple point, at which a solid, liquid and vapor coexist in equilibrium. The circle represents the pure component critical point, where the supercritical region begins. 

The SAFT equation of state typically contains five pure compound parameters, which are estimated from both vapor pressure and liquid density data. These are the molecular size parameter m, the segment size parameter v, the segment energy parameter u°lk, and the two association parameters the association energy e /k and the association volume. ... 

The NIST s Thermodynamics Research Center (TRC) has a large collection of pure-fluid thermodynamic and transport properties tables of recommended values and correlations exist both in paper form and in a computer database [12], The TRC has also produced books with comprehensive compilations for organic compounds (sometimes also available as software) for vapor pressure [17], liquid density [18], and ideal-gas heat capacity [29], in addition to a compilation on virial coefficients [32]. Their major archival database of experimental pure-component and mixture data is called Source [97] it is currently available only to members of their consortium. Some data for mixtures of organic compounds are published in the periodical Selected Data on Mixtures [49]. More information is at http //trc.nist.gov. 

Although Lord Kelvin developed the nation describing the relationship between the vapor pressure of liquids immobilized in pores and pore diameter in the late nineteen hundr, it was not verified until 1979 (2). Fisher verified the Kelvin equation only for pure liquids. It is not clear what effect small capillaries would have on the vapor pressure or solutions, although, some litoature CD suggests that the vapor pressure suppression effect should be synergistically oihanced with the presence of solutes. 

It is important to note that in these calculations, it is assumed that the solute is in a dissolved form in both phases i.e., it is not present in sorbed, micelle, or colloidal forms. The concentrations must, of course, be less than the saturation values, which correspond to the solubility of the substance in the water phase and to the vapor pressure in the atmosphere. A convenient method of calculating Henry s constants is to express H as the ratio of the solute s saturation vapor pressure P as obtained from handbooks, to the solute s aqueous solubility C It is important that the state of the two phases (i.e., solid or liquid) be the same for both data. This has caused problems with PCBs in which the available solubility data tend to be those of the pure solid isomers, whereas the vapor pressure data are obtained by extrapolation from vapor pressures of liquid mixtures. It is essential that the two sets of data apply to the same solute physical condition. 

Here is the vapor pressure of pure liquid solute at the same temperature and total pressure as the solution. If the pressure is too low for pure B to exist as a liquid at this temperature, we can with little error replace with the saturation vapor pressure of liquid B at the same temperature, because the effect of total pressure on the vapor pressure of a liquid is usually negligible (Sec. 12.8.1). If the temperature is above the critical temperature of pure B, we can estimate a hypothetical vapor pressure by extrapolating the liquid-vapor coexistence curve beyond the critical point. 

To illustrate this approach, we shall determine an expression of the vapor pressure of liquid copper at temperature T, which is above its fusion point of 1357 K. As a reference state, we choose the standard state of the pure substance at a temperature of 298 K and pressure of 1 bar. We have the following data ... 

In this chapter, we explore some properties of pure liquids and solids. VVe model the vapor pressures over liquids and the processes of boiling and sublimation. This is the foundation for treating solvation effects in chemical and physical equilibria in Chapters 15 and 16. 

Two constant equations of state can be fitted to specific fluid properties in the two-phase region up to and including the critical. However, if this is done, considerable accuracy is lost when calculating other fluid properties not used in the fitting process i.e., if pure component vapor pressures and liquid phase densities up to the critical point and equality of vapor and liquid phase fuga-cities are used to determine the two constants, then properties such as enthalpy correction and the derlvatles of (3P/9v.p) at or near the critical point will be incorrect. These equations of state do not have a sufficient number of independent variables to fit all properties correctly. 

The melting temperature of pure iron at 1 atm is 1535°C 1808K. At that temperature the vapor pressure of liquid and of solid iron are the same. 

Partial Vapor Pressures of Liquid Components. Just as each component of a vapor exerts a partial pressure, each component of a liquid exerts a partial vapor pressure. This is dependent upon the concentration of the component in the liquid and the vapor pressuie of the pure component. The escaping tendency of a component appears to depend upon the percentage of the surface area (mole frarction) covered by the component and the molecul tenergy (vapor pressure) of the component. If P is the vapor pressure of the pure component at a given temperature and X is the mole fraction of the same component in the liquid,... 

American Petroleum Institute, Bibliographies on Hydrocarbons, Vols. 1-4, "Vapor-Liquid Equilibrium Data for Hydrocarbon Systems" (1963), "Vapor Pressure Data for Hydrocarbons" (1964), "Volumetric and Thermodynamic Data for Pure Hydrocarbons and Their Mixtures" (1964), "Vapor-Liquid Equilibrium Data for Hydrocarbon-Nonhydrocarbon Gas Systems" (1964), API, Division of Refining, Washington. 

Enthalpies are referred to the ideal vapor. The enthalpy of the real vapor is found from zero-pressure heat capacities and from the virial equation of state for non-associated species or, for vapors containing highly dimerized vapors (e.g. organic acids), from the chemical theory of vapor imperfections, as discussed in Chapter 3. For pure components, liquid-phase enthalpies (relative to the ideal vapor) are found from differentiation of the zero-pressure standard-state fugacities these, in turn, are determined from vapor-pressure data, from vapor-phase corrections and liquid-phase densities. If good experimental data are used to determine the standard-state fugacity, the derivative gives enthalpies of liquids to nearly the same precision as that obtained with calorimetric data, and provides reliable heats of vaporization. 

This chapter presents quantitative methods for calculation of enthalpies of vapor-phase and liquid-phase mixtures. These methods rely primarily on pure-component data, in particular ideal-vapor heat capacities and vapor-pressure data, both as functions of temperature. Vapor-phase corrections for nonideality are usually relatively small. Liquid-phase excess enthalpies are also usually not important. As indicated in Chapter 4, for mixtures containing noncondensable components, we restrict attention to liquid solutions which are dilute with respect to all noncondensable components. 

CALCULATE PURE COMPONENT LIQUID FUGACITY AT SPECIFIED TEMP AND ZERO PRESSURE IF IVAP.LE.2 C PURE CCMPDNENT VAPOR PRESSURE IF IVAP.EQ.3... 

The calculation of vapor pressure of a pure substance consists of finding the pressure for which the fugacities of the liquid and vapor are equal. 

Adsorption may occur from the vapor phase rather than from the solution phase. Thus Fig. Ill-16 shows the surface tension lowering when water was exposed for various hydrocarbon vapors is the saturation pressure, that is, the vapor pressure of the pure liquid hydrocarbon. The activity of the hydrocarbon is given by its vapor pressure, and the Gibbs equation takes the form... 

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