Thermodynamics vapor pressure measurements

Thermodynamic. The thermodynamic properties of elemental plutonium have been reviewed (35,40,41,43—46). Thermodynamic properties of sohd and Hquid Pu, and of the transitions between the known phases, are given in Table 5. There are inconsistencies among some of the vapor pressure measurements of Hquid Pu (40,41,43,44). 

Carmona, F.J., Gonzalez, J.A., Carcia de la Fuente, I., Cobos, J.C., Bhethanabotla, V.R., Campbell, S.W. (2000) Thermodynamic properties of n-alkoxyethanols + organic solvent mixtures. XI. Total vapor pressure measurements for n-hexane, cyclohexane or n-hcptanc + 2-ethoxyethanol at 303.15 and 323.15 K. J. Chem. Eng. Data 45, 699-703. 

A large number of investigations have been reported on spectroscopic, thermodynamic, and other equilibrium properties of chalcogen tetrahalides (e.g., 158-162). They include vibrational spectroscopic analyses of SeCU and TeCU in the solid on the basis of the known structures 89, 373) and in the gas phase (37), equilibrium measurements of SeCU and TeCU in molten salts (f12,376,422), determination of enthalpies of formation 335, 339, 433), other equilibrium studies, and determination of thermodynamic data from vapor pressure measurements, mass spectrometric investigations, conductivity experiments, and thermal phase analysis in the solid (37, 39,203,275, 333, 337, 339, 340, 341, 342,379, 402, 403). 

The possibility of calculating thermodynamic functions from infrared and Raman frequencies has been exploited for Fe(05115)2, Ni(OsH5)2, and Ru(OsH6)2 (124)- The vapor-pressure curve of ferrocene was also reported soon after its discovery (112). Vapor-pressure measurements for dicyclopentadienyl manganese are also available (216). The heats of formation of Fe(05Hs)2 and Ni (05115)2 from the O5H6 radical and the... 

Thermodynamic properties of the ideal monatomic gas have been calculated from the spectroscopic information reported by Moore 341) Vapor pressure measurements have been made by Douglas (55), Hartmann and Schneider 14 )f Pilling 361), Priselkov and... 

Evans, Jacobson, Munson, and Wagman (105) have calculated the thermodynamic properties of the ideal monatomic and diatomic gases and list 10,380 cal./mole for the heat of dissociation of the diatomic gas. Vapor pressure measurements have been made by Scott (290), Ruff and Johannsen (281), Taylor and Langmuir (324), Fuchtbauer and Bartels (116), Kroner (204), and by Hackspill (141)- The data of the last four sets of workers are in excellent agreement, and lead to a heat of sublimation at 298 K. of 18,670 cal./gram atcm for the ideal monatomic species, 26,630 cal./mole for the ideal diatomic species, a norn al boiling point of 958 K., and a heat of vaporization to equilibrium vapor at 958 K. of 15,750 cal./gram atom. 

Thermodynamic functions for the ideal monatomic gas have been calculated from spectroscopic data given by Moore (241). Older vapor pressure measurements of Harteck (145) and of Marshall, Dornte, and Norton (223) agree with the more recent measurements of Hersh (151) and of Edwards, Johnston, and Ditmars (99). From these data we find the heat of sublimation at 298 K. to be 81,100 cal./gram atom, a normal boiling point of 2855 K., and a heat of vaporization at 2iS55 K. of 72,800 cal./gram atom. 

Stephenson reports the entropy of the red triclinic crystals at 298° K. as 5.46 e. u. Farr has reported the heat capacity of this form to the sublimation point as well as a melting point of about 870° K. Spectroscopic data by Moore (341) on the monatomic species and by Herzberg (1S3,153) for the diatomic and tetratomic species have been used to compute the thermodynamic functions of the ideal monatomic, diatomic, and tetratomic gases. From vapor pressure measurements reported by Farr, we calculate the... 

The real occurrence of polymerization inside the channels was demonstrated in several ways. It does not occur, at least for a number of monomers, when there is a simple mixture of host and monomer without the formation of a clathrate or when the monomer is placed in the presence of solid substances unable to form inclusion compounds. Even in cases when polymerization does take place the structure of the polymer formed outside the channels differs from that obtained in proper conditions. The reaction rate is very temperature and pressure dependent and has a sheirp drop-off point beyond which reaction ceases. The boundaur y conditions for polymerization correspond to those which delimit the field of thermodynamic stability of the monomeric clathrate, determined by vapor pressure measurements or by DSC. This coincidence enables us to state that the two phenomena, monomer inclusion and polymerization, are strictly related. In addition, in some typical cases a structural change from monomer to polymer was directly observed inside the channels by X-ray analysis. 

Equation (2) can only be used for the pressure determination if there is molecular flow in the effusion orifice of the Knudsen cell. According to Boer-boom [30] molecular flow exists as a coarse approximation for p < 3.6/r (p in Pa, r in mm), where p is the pressure in the Knudsen cell and r is the radius of the effusion orifice. The demand for a molecular flow and the effusion orifice diameter thus determines the upper limit of the range for the vapor pressure measurement. Experimental and theoretical studies on the transition range between molecular and hydrodynamic flow were recently reviewed by Wahl-beck [89] and references quoted therein. Thermodynamic studies at the limit of the Knudsen flow region are discussed by Hiipert and Gingerich [80]. 

Initially, the vapor pressure measurements appear to be the most direct, but even here some assumptions are needed. The amount of alcohol in the micellar phase needs to be determined. To do this the difference in vapor pressure between a pure aqueous and a micellar solution is measured. If the ions of the surfactant salts out alcohol, the vapor pressure of pure water is not the correct comparison, and this could lead to lower partition coefficients. Thermodynamic data are well suited for model calculations, and both the models of DeLisi et al. ° ° and Hetu et al. fit the data well. Although in reasonable internal agreement, the partition coefficients calculated from partial molar volumes differ from those calculated from enthalpies the first is 927 or 944, the latter... 

The importance of these observations lies in the fact that the 298 value is the basis point for the free-energy functions for both the solid and the gas. With a reasonably accurate estimate of the solid crystal entropy, the gaseous spectroscopic data and precise vapor pressure measurements, it is possible to calculate all the thermodynamic values for the metal, up to the highest temperatures of measurement. Also, a self-consistent heat capacity curve starting at 298 K is produced for the intensely-radioactive and scarce trans-curium metals, normal calorimetry may never be possible, and these techniques become extremely important tools. A detailed example of a typical calculation will be given under Californium below. 

Head-space gas chromatography is a modem tool for the measurement of vapor pressures in polymer solutions that is highly automated. Solutions need time to equilibrate, as is the case for all vapor pressure measurements. After equihbration of the solutions, quite a lot of data can be measured continuously with reliable precision. Solvent degassing is not necessary. Measurements require some experience with the equipment to obtain really thermodynamic equihbrium data. Calibration of the equipment with pure solvent vapor pressures may be necessary. HSGC can easily be extended to multi-component mixtures because it determines all components in the vapor phase separately. 

Osmotic pressure is a thermodynamic property of the solution. Thus, n is a state variable that depends upon temperature, pressure, and concentration but does not depend upon the membrane as long as the membrane is semipermeable. Osmotic equilibrium requires that the chemical potentials of the solvent on the two sides of the membrane be equal. Note that the solutes are not in equilibrium since they cannot pass through the membrane. Although osmotic pressure can be measured directly, it is usually estimated from other measurements (e.g., Reid, 1966). For an incompressible liquid osmotic pressure can be estimated from vapor pressure measurements. 

The measurement of polymer solutions with lower polymer concentrations requires very precise pressure instruments, because the difference in the pure solvent vapor pressure becomes veiy small with decreasing amount of polymer. At least, no one can really answer the question if real thermodynamic equilibrium is obtained or only a fro2en non-equihbrium state. Non-equilibrium data can be detected from imusual shifts of the %-function with some experience. Also, some kind of hysteresis in experimental data seems to point to non-equilibrium results. A common consistency test on the basis of the integrated Gibbs-Duhem equation does not work for vapor pressiue data of binary polymer solutions because the vapor phase is pme solvent vapor. Thus, absolute vapor pressure measurements need very careful handling, plenty of time, and an experienced experimentator. They are not the method of choice for high-viscous polymer solutions. 

Since (j)i and vapor pressure measurement. The two other thermodynamic parameters, AHi and A5i, can be calculated using the following equations ... 

It follows from Tables 284 1 that the convergence of the AsubH°(298, III law) and Asubff°(298, II law) values obtained in our calculations is quite satisfactory. A total of 114 saturated vapor pressure measurements were performed for 14 of the 15 lanthanide trichlorides (all except PmCla). These values were used to calculate the enthalpies of sublimation by the second and third laws of thermodynamics simultaneously. Of these 114 results, 39 were obtained for vapor pressures over solids and 75 for vapor pressures over liquid samples. 

---