Data analysis vapor pressure measurement

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). 

AjH° is calculated from that of the crystal by means of A H°(298.15 K) = 55.15 0.1 kcal mol". The selected value of sub ° is an average of those obtained by 3rd law analysis of vapor pressures measured by manometry ( ), torsion effusion (4) and entrainment (8-10). Mass-spectrometric data (, 2) are in reasonable agreement and so is the average of two Knudsen-effusion studies (6, 7). Several techniques (2, 4, 6) were used to show that the amount of dimer in the vapor is negligible up to at least 1000 K. JANAF analyses of the vaporization data are summarized as follows ... 

The first reliable spectroscopic analysis of saturated sulfur vapor was published by Berkowitz and Marquart [28] who used a combination of a Knud-sen effusion cell with a mass spectrometer and generated the sulfur vapor by evaporating either elemental sulfur (low temperature region) or certain metal sulfides such as HgS which decompose at high temperatures to sulfur and metal vapor. These authors observed ions for all molecules from S2 to Ss and even weak signals for Sg and Sio. From the temperature dependence of the ion intensities the reaction enthalpies for the various equilibria (1) were derived (see Table 1). Berkowitz and Marquart careMly analyzed their data to minimize the influence of fragmentation processes in the ion source of the spectrometer. They also calculated the total pressure of sulfur vapor from their data and compared the results with the vapor pressure measurements by Braune et al. [26]. The agreement is quite satisfactory but it probably... 

Pankow, J. F., and T. F. Bidleman, Interdependence of the Slopes and Intercepts from Log-Log Correlations of Measured Gas-Particle Partitioning and Vapor Pressure—I. Theory and Analysis of Available Data, Atmos. Environ., 26A, 1071-1080 (1992). 

Pankow JF, Bidleman TF (1992) Interdependence of the slopes and intercepts from log-log correlations of measured gas-particle partitioning and vapor pressure-I. Theory and analysis of available data. Atmos Environ 26A(6) 1071-1080... 

Look It Up. When you need a value for a physical property of a substance—whether it be a density, vapor pressure, solubility, or heat capacity—there is a good chance that someone, somewhere has measured this property and published the result. Since experiments are usually costly and time consuming, a reliable source of physical property data is an invaluable asset in process analysis. Four excellent sources of data are the following ... 

AjH (LlBr, g, 298.15 K) -36.8 3 kcal mol" (-153.971 13 kJ mol"" ) Is calculated from the selected enthalpy of vaporization and the enthalpy of formation for lithium bromide (t). Lithium bromide vaporizes to a mixture of monomeric and dimeric gases. (Higher polymers have been neglected In the calculation.) The enthalpies of vaporization to monomer and to dimer were chosen to satisfy (1) the total vapor pressure data measured by von Wartenberg and Schulz (1 ) and by Ruff and Mugdan (2) the partial vapor pressures of monomer and dimer derived from Miller and Kusch (3 ) In an analysis of the velocity distribution of molecules In... 

The vapor pressures over NbBrg(cr, ) have been measured by Alexander and Fairbrother (1 ) and Berdonosov et al. (2). A 2nd and 3rd law analysis of their data is given below. The enthalpy of formation for NbBrg(g) is derived from the sublimation... 

Drowart et al. (1 ) have measured mass spectrometrically the ion intensity ratio fC as a function of temperature from 1800 to 2700 K. We derive from a 2nd law analysis of their data a H (2200 K) = 185.2 3.3 kcal, and S (2200 K) 74.9 2.8 cal K" mol" by calculation of the absolute pressure from the vapor pressure of monatomic carbon and a relative ionization cross-section ratio of 2.3. The entropy uncertainty includes 1.3 cal k" mol for uncertainty in the absolute pressure. Several earlier mass-spectrometric determinations (2, 3, 4) are in reasonable agreement. The absolute magnitude of the... 

The heat of sublimation was determined by second and third law analysis of the following vapor pressure data. Magee (1 ) measured both vapor pressure by torsion effusion and vapor density in the range 533-644 K and found only trimer present. The second and third law analyses gave A. H (298.15 K) = 37.37 0.04 and 37.24 0.02 kcal mol" with a drift of -0.25 0.07 cal K" ... 

The enthalpy of formation for Ni(g) is obtained by an analysis of the vapor pressure data of Morris et al. ( ). In this study a gas-transport method was used to measure vapor pressures (16 points) over liquid nickel in the range 1816-1895 K. For... 

Determination of solubility by headspace analysis offers several advantages over spectrophotometric techniques. First, because of the selectivity of chromatographic analysis, compound purity is not a critical factor second, absolute calibration of the gas chromatographic detector is not necessary if the response is linearly related with concentration over the range necessary for the measurements and finally, this method does not require the preparation of saturated solutions, since a partition coefficient, not a solubility, is actually measured. However, headspace methodology would probably not be applicable for determining PAH solubilities for three reasons. First, there is little data in the literature on the vapor pressures of PAHs. Second, the aqueous solubilities of most PAHs are too low to be measured by this procedure. Finally, adsorptive losses of PAHs to glass surfaces from the vapor phase would cause errors. 

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