Vapour pressure measurement

Sb2l4 is much less stable it has been detected by emf or vapour pressure measurements on solutions of Sb in Sbl3 at 230° but has not been isolated as a pure compound. 

There is fair agreement between the two sets, considering the difficulty of the vapour-pressure measurements. 

Measurements in this held have been made by Berthelot and Ogier with nitrogen tetroxide Ann. de Chim. et Phys., [v.], 30, 382 (1883)), and with acetic acid ibid., 400), and some calculations with reference to steam have been made by Nernst Verhandl. Deutsch. Phys. Ges., 15, 313) and Levy ibid., 330), who utilised the vapour-pressure measurements of Holborn and Henning Ann. der Physik, (1906), 21 (1907), 22, 23). Wiedemann had previously observed that the specific heats of ethylbromide, ethyl-acetate, and benzene increase with temperature at about the same rate as that of nitrogen tetroxide at 200°. In the case of steam it was assumed that (i.) the polymerisation is to double molecules... 

The values of i calculated from (8) and (8) do not agree very closely, and it would appear, as Weinstein (loc. cit. 1068) remarks, that Although the calculations undoubtedly establish the legitimacy of the system of equations, the great uncertainty in the numerical determination of the decisive magnitudes forms a practical defect which will only be removed by observations over very wide intervals of the variables. Any discrepancy between the results of actual observations of equilibria, and those calculated by means of Nernst s chemical constants, need not, in the present state of uncertainty of the latter, cause any great alarm. Nernst himself apparently regards the constant < >, obtained from vapour-pressure measurements, as the most certain, and the others as more or less tentative. 

Elmore, K. L., Mason, C. M. Christensen, J. H. (1946). Activity of orthophosphoric acid in aqueous solutions at 25 °C from vapour pressure measurements. Journal of the American Chemical Society, 68, 2528-32. 

A detailed discussion of the problems encountered in vapour pressure measurements at low temperature is given in ref. [46,47], where also the use of an in situ manometer is described. Vapour pressure gas thermometry with other liquids besides He is discussed in ref. [43, p. 49],... 

Balson, E. W. (1947) Studies in vapour pressure measurement. Part in. An effusion manometer sensitive to 5 x 10 6 millimetres of mercury vapour pressure of D.D.T. and other slightly volatile substances. Trans. Farad. Soc. 43, 54—60. 

Piacente, V., Pompili, T., Scardala, P., Ferro, D. (1991) Temperature dependence of the vaporization enthalpies of n-alkanes from vapour-pressure measurements. J. Chem. Thermodyn. 23, 379-396. 

Van der Linde, P.R., Blok, J.G., Oonk, AJ. (1998) Naphthalene as a reference substance for vapour pressure measurements looked upon from an unconventional point of view. J. Chem. Thermodyn. 30, 909-917. 

Van Ekeren, P.J., Jacobs, M.H.G., Offringa, J.C.A., De Kruif, C.G. (1983) Vapour-pressure measurements on rnms-diphenylethenc and naphthalene using a spinning-rotor friction gauge. J. Chem. Thermodyn. 15, 409—417. 

Bouldoires, J. R Experimental study of heat and mass transfer during freeze-drying through dielectric and vapour pressure measurements, p. 189-206. International Institute of Refrigeration (Comm. X, Lausanne, 1969)... 

B. Determination of the Basicity from Vapour Pressure Measurements. 238... 

B. determination of the basicity by means of vapour pressure measurements, and... 

It follows from the above considerations that it is necessary to use systems of greater acidity in order to study the formation of proton addition complexes by means of vapour pressure measurements. As with the partition equilibria discussed under IIIA, the systems HF -I- NaF (or KF) and HF -h BFg -f- NaBF4 have again to be considered. 

The methods for the determination of the basicity of aromatic compounds discussed hitherto have as their starting point the formation of a proton addition complex in an acid solution. In addition to this interaction, numerous intermolecular interactions are known which are also directly connected with the basicity of unsatimated compounds but which do not lead to the formation of a true covalent bond. This interaction was already mentioned in connection with the vapour pressure measurements of the system of aromatic substance-HCl, and leads to a 77--complex (Dewar, 1946). 

The iT-values show clearly that the mesitylene-iodine complex is more stable than the benzene-iodine complex. The ratio of the T-values of the two complexes corresponds roughly to the ratio of the. K -values obtained from an evaluation of vapour pressure measurements (Table 9). It must, however, be borne in mind that these measurements were carried out at very different temperatures, so that this comparison is only a qualitative one. 

If a halogen atom is substituted into the benzene nucleus in place of a methyl group, then the basicity decreases and falls below the value for benzene. O Brien and collaborators (1939 O Brien and Kenny, 1940 O Brien and Byrne, 1940 O Brien, 1942) found the following order from vapour pressure measurements ... 

Generally, vapour pressure measurements are fitted to a form of the Clausius-Clapeyron equation ... 

The electromotive force (EMF) generated by electrochemical cells can be used to measure partial Gibbs energies which, like vapour pressure measurements, distinguishes these methods from other techniques that measure integral thermodynamic quantities. Following Moser (1979), a typical cell used to obtain results on Zn-ln-Pb is represented in the following way ... 

EMF and vapour pressure measurements are dependent on the temperature, the number of phases involved and, importantly, the reference state of the component in question. The problem with the reference state is important as experimentally stated values of partial Gibbs energies will be dependent on this value. The standard states are fixed before optimisation and may actually have values different from those used by the original author. Therefore, as far as possible like should be compared with like. 

If vapour pressure measurements are to be an essential part of the work to be undertaken, a cold cathode manometer is probably the best choice, despite the fact that it needs to be calibrated for each molecular species, and its use with mixtures of gases containing two or more species is correspondingly more difficult. If such mixtures are to be investigated, or if the chemicals concerned are corrosive, it is probably most efficient to use a mechanical gauge as a null-point instrument and to measure the pressure by means of a McLeod gauge. 

Diammino-mercuric Iodide, [Hg(NH3)2]I2, behaves like the ammines of zinc and loses ammonia on exposure to air the mon-ammino derivative from examination of vapour-pressure measurements does not appear to exist. 

When heated under ordinary pressure, arsenic does not melt the metallic form volatilises at a dull red heat, while amorphous arsenic does so at a lower temperature. The sublimation temperatures are given on p. 32. Even at ordinary temperature the element possesses an appreciable vapour pressure, as may be shown 8 by enclosing pieces of arsenic and silver in a vessel, but not in contact with each other after some months the silver is found to be coated with a film of arsenide. Vapour pressure measurements of grey metallic arsenic and its liquid at temperatures up to 853° C. have been made the results, expressed in atmospheres, are as follows ... 

Vapour pressures for a number of atmospherically relevant condensed systems have been measured with mass spectrometry. These systems include hydrates of HC1, HjS04 and HNO, supercooled liquids and pure water-ice, as well as the interactions of HC1 vapour with die solids, ice and NAT [23,47,50-55]. Vapour pressure measurements over HNOj/HjO hydrates have also been made using infrared optical absorption with light originating from a tunable diode laser [29]. This technique allowed the identification of the metastable NAD in presence of the more stable NAT under temperature and vapour pressure conditions near to those found in the polar stratosphere. Vapour pressures of Up, HN03, HC1, HBr over supercooled aqueous mixtures with sulfuric acid have been calculated using an activity model [56]. It provides a parameterized model for vapour pressures over the stratospheric relevant temperatures (185-235 K). 

Turning to the kinetics, we start with the difference in the free energy of activation in methanol and in water, (AGt MeOH — AGt H °). One has to separate out the effect of the transfer of the reactant. These values can be found from vapour pressure measurements (Abraham and Johnston, 1971). It is then possible to calculate the free energy of transfer of the transition state from water to methanol according to (72). Figure 16 illustrates the terms in... 

Thermochemistry DSC (see Box 9.1) TGA (see Box 9.1) Vapour pressure measurements Solid-state NMR Ultramicroscopy Scanning electron microscopy (SEM) Tunnelling electron microscopy (TEM) Atomic force microscopy (AFM) Molecular dynamics... 

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