The Pure Liquid

For such components, as the composition of the solution approaches that of the pure liquid, the fugacity becomes equal to the mole fraction multiplied by the standard-state fugacity. In this case,the standard-state fugacity for component i is the fugacity of pure liquid i at system temperature T. In many cases all the components in a liquid mixture are condensable and Equation (13) is therefore used for all components in this case, since all components are treated alike, the normalization of activity coefficients is said to follow the symmetric convention. ... 

In a binary liquid solution containing one noncondensable and one condensable component, it is customary to refer to the first as the solute and to the second as the solvent. Equation (13) is used for the normalization of the solvent s activity coefficient but Equation (14) is used for the solute. Since the normalizations for the two components are not the same, they are said to follow the unsymmetric convention. The standard-state fugacity of the solvent is the fugacity of the pure liquid. The standard-state fugacity of the solute is Henry s constant. 

Chapter 3 discusses calculation of fugacity coefficient < ). Chapter 4 discusses calculation of adjusted activity coefficient Y fugacity of the pure liquid f9 [Equation (24)], and Henry s constant H. 

Figure 1 gives an enthalpy-concentration diagram for ethanol(1)-water(2) at 1 atm. (The reference enthalpy is defined as that of the pure liquid at 0°C and 1 atm.) In this case both components are condensables. The liquid-phase enthalpy of mixing... 

Enthalpies are referred to zero enthalpies of the pure liquids. at 1.013 bars and 273.2 K. 

The constants in Equation (5) are not the same as those in Equation (4). Using this saturation pressure, the pure-liquid reference fugacity at zero pressure is then calculated from the equation... 

The partial fugacity of component i in the liquid phase is expressed as a function of the total fugacity of this same component in the pure liquid state, according to the following relation ... 

C , = average specific heat of the pure liquid between... 

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... 

A complication now arises. The surface tensions of A and B in Eq. IV-2 are those for the pure liquids. However, when two substances are in contact, they will become mutually saturated, so that 7a will change to 7a(B) and 7b to 7B(A). That is, the convention will be used that a given phase is saturated with respect to that substance or phase whose symbol follows in parentheses. The corresponding spreading coefficient is then written 5b(A)/a(B)-... 

The present discussion is restricted to an introductory demonstration of how, in principle, adsorption data may be employed to determine changes in the solid-gas interfacial free energy. A typical adsorption isotherm (of the physical adsorption type) is shown in Fig. X-1. In this figure, the amount adsorbed per gram of powdered quartz is plotted against P/F, where P is the pressure of the adsorbate vapor and P is the vapor pressure of the pure liquid adsorbate. 

The adsorbed state often seems to resemble liquid adsorbate, as in the approach of the heat of adsorption to the heat of condensation in the multilayer region. For this reason, a common choice for the standard state of free adsorbate is the pure liquid. We now have... 

The composition of the vapour can easily be calculated as follows — Assuming that the gas laws are applicable, it follows that the number of molecules of each component in the vapour wdll be proportional to its partial pressure, i.e., to the vapour pressure of the pure liquid at that temperature. If and p are the vapour pressures of the two liquids A and B at the boiling point of the mixture, then the total pressure P is given by ... 

In addition to the orthodox method, just described, for the determination of the boiling points of liquids, the student should determine the boiling points of small volumes (ca. 0 5 ml.) by Siwolobofifs method. Full details are given iri Section 11,12. Determine the boiling points of the pure liquids listed in the previous paragraph. Observe the atmospheric pressure and if this differs by more than 5 mm. from 760 mm., correct the boiling point with the aid of Table II,9,B. Compare the observed boiling points with the accepted values, and draw a calibration curve for the thermometer. 

The conclusion of all these thermodynamic studies is the existence of thiazole-solvent and thiazole-thiazole associations. The most probable mode of association is of the n-rr type from the lone pair of the nitrogen of one molecule to the various other atoms of the other. These associations are confirmed by the results of viscosimetnc studies on thiazole and binary mixtures of thiazole and CCU or QHij. In the case of CCU, there is association of two thiazole molecules with one solvent molecule, whereas cyclohexane seems to destroy some thiazole self-associations (aggregates) existing in the pure liquid (312-314). The same conclusions are drawn from the study of the self-diffusion of thiazole (labeled with C) in thiazole-cyclohexane solutions (114). 

IR spectra can be recorded on a sample regardless of its physical state—solid liquid gas or dissolved m some solvent The spectrum m Eigure 13 31 was taken on the neat sample meaning the pure liquid A drop or two of hexane was placed between two sodium chloride disks through which the IR beam is passed Solids may be dis solved m a suitable solvent such as carbon tetrachloride or chloroform More commonly though a solid sample is mixed with potassium bromide and the mixture pressed into a thin wafer which is placed m the path of the IR beam... 

Let us now consider the process of capillary condensation. For the pure liquid (a) in equilibrium with its vapour fi), the condition for mechanical equilibrium is given by Equation (3.6) and that for physicochemical equilibrium by... 

Lj and are the pure liquid and inert gas loading rates, respectively, in units of Ib-moles/hr-ft. The second expression is the operating line on an equilibrium diagram. In all scrubbing application, where the transfer of solute is from the gas to the liquid, the operating line will lie above the equilibrium curve. When the mass transfer is from the liquid to the gas phase, the operating line will lie below the equilibrium curve. The latter case is known as stripping . 

Boiling in the bulk of the fluid generally takes place at submicron nucleation sites as impurities, crystals, or ions. When there is a shortage of nucleation sites in the bulk of the liquid, its boiling point can be exceeded without boiling then the liquid is superheated. There is, however, a limit at a given pressure above which a liquid cannot be superheated, and when this limit is reached, microscopic vapor bubbles develop spontaneously in the pure liquid (without nucleation sites). 

For the condensation, without mixing, of the pure liquids, the energy change would be... 

The molecular orbital description of the bonding in NO is similar to that in N2 or CO (p. 927) but with an extra electron in one of the tt antibonding orbitals. This effectively reduces the bond order from 3 to 2.5 and accounts for the fact that the interatomic N 0 distance (115 pm) is intermediate between that in the triple-bonded NO+ (106 pm) and values typical of double-bonded NO species ( 120 pm). It also interprets the very low ionization energy of the molecule (9.25 eV, compared with 15.6 eV for N2, 14.0 eV for CO, and 12.1 eV for O2). Similarly, the notable reluctance of NO to dimerize can be related both to the geometrical distribution of the unpaired electron over the entire molecule and to the fact that dimerization to 0=N—N=0 leaves the total bond order unchanged (2 x 2.5 = 5). When NO condenses to a liquid, partial dimerization occurs, the cis-form being more stable than the trans-. The pure liquid is colourless, not blue as sometimes stated blue samples owe their colour to traces of the intensely coloured N2O3.6O ) Crystalline nitric oxide is also colourless (not blue) when pure, ° and X-ray diffraction data are best interpreted in terms of weak association into... 

Despite these reaction products there is little evidence for an ionic self-dissociation equilibrium in liquid CIF3 such as may be formally represented by 2CIF3 V— CIF2 + C1F4, and the electrical conductivity of the pure liquid (p. 828) is only of the order of 10 ohm cm. The structures of these ions are discussed more fully in subsequent sections. 

In addition to its use as a straight fluorinating agent, BrF3 has been extensively investigated and exploited as a preparative nonaqueous ionizing solvent. The appreciable electrical conductivity of the pure liquid (p. 828) can be interpreted in terms of the dissociative equilibrium... 

The chemical reactions of IF5 have been more extensively and systematically studied because the compound can be handled in glass apparatus and is much less vigorous a reagent than the other pentafluorides. The (very low) electrical conductivity of the pure liquid has been ascribed to slight ionic dissociation according to the equilibrium... 

The refractive index of a medium is the ratio of the speed of light in a vacuum to its speed in the medium, and is the square root of the relative permittivity of the medium at that frequency. When measured with visible light, the refractive index is related to the electronic polarizability of the medium. Solvents with high refractive indexes, such as aromatic solvents, should be capable of strong dispersion interactions. Unlike the other measures described here, the refractive index is a property of the pure liquid without the perturbation generated by the addition of a probe species. 

It was quite recently reported that La can be electrodeposited from chloroaluminate ionic liquids [25]. Whereas only AlLa alloys can be obtained from the pure liquid, the addition of excess LiCl and small quantities of thionyl chloride (SOCI2) to a LaCl3-sat-urated melt allows the deposition of elemental La, but the electrodissolution seems to be somewhat Idnetically hindered. This result could perhaps be interesting for coating purposes, as elemental La can normally only be deposited in high-temperature molten salts, which require much more difficult experimental or technical conditions. Furthermore, La and Ce electrodeposition would be important, as their oxides have interesting catalytic activity as, for instance, oxidation catalysts. A controlled deposition of thin metal layers followed by selective oxidation could perhaps produce cat-alytically active thin layers interesting for fuel cells or waste gas treatment. 

Clausius-Clapeyron Equation. This equation was originally derived to describe the vaporization process of a pure liquid, but it can be also applied to other two-phase transitions of a pure substance. The Clausius-Clapeyron equation relates the variation of vapor pressure (P ) with absolute temperature (T) to the molar latent heat of vaporization, i.e., the thermal energy required to vajxirize one mole of the pure liquid ... 

Hydrophobicity represented by AG° for the transfer of solute from the pure liquid to aqueous solution increases progressively with increasing temperature34>. There is, however, an extremum in the temperature—selectivity plot in some cases (e.g., R2 = i-CsHn, Ph, and p-MeC6H4) l4b,18). it appears that the observed selectivity cannot be explained in terms of hydrophobic interaction. 

---