Ethyl alcohol vapour pressure

Rossini (Bur. Stand. J. Res. 1932, 8, 119) burnt a mixture of ethyl alcohol vapour and air at constant pressure in a reaction vessel inside a calorimeter. He measured the heat evolved and the mass of carbon dioxide formed. From his measurements we have... 

It is desired to concentrate a mixture of ethyl alcohol and water from 40 mole per cent to 70 mole per cent alcohol. A continuous fractionating column, 1.2 m in diameter with 10 plates is available. It is known that the optimum superficial vapour velocity in the column at atmosphere pressure is 1 m/s, giving an overall plate efficiency of 50 per cent. 

Apart from the fact that the layer is very thin and that its vapour pressure is equal to that of the wet lens, no definite information is available on this point. On the other hand, in the case of ethyl alcohol, acetic and the lower fatty acids, we have noted already that a tightly packed unimolecular layer is readily obtained long before the vapour pressure above the solution is equal to that of the pure alcohol (since Fmax. is obtained in this case at 0 3 molar) or acid. Thus for these substances to obtain equality of vapour pressure between a surface and bulk phase, layers more than one molecule thick must be necessary. 

References are appended to investigations of the optical properties16 of the crystalline forms to such properties of the aqueous solution as vapour-pressure,17 density,18 molecular depression of the freezing-point,19 electric conductivity,20 and index of refraction 21 and to the solubility in ethyl alcohol.22... 

Physical and Chemical Properties It is a colourless liquid with a pungent odour and boils at ordinary pressure at 133° to 135° C. with decomposition. At 16 mm. pressure it distils unaltered at 42° C. It melts at — 70° C. and has a S.G. at 15° C. of 1-492, while its vapour density is 4-5 (air = i). The volatility at 20° C. is 60,000 mgm. per cu. m. It is immiscible with sulphuric acid, but miscible with carbon tetrachloride, chloroform and ethyl alcohol. It is insoluble in water, which hydrolyses it according to the equation ... 

The following pairs have neither a maximum nor a minimum vapour pressure water and acetone, ethyl alcohol and acetone, ethyl alcohol and carbon disulphide, acetic acid and benzene, ether and benzene, etc. The following pairs have rectihnear vapour pressure curves benzene and chlorbenzene, benzene and brombenzene, toluene and chlorbenzene, ethylene bromide and propylene bromide. Thus, for very similar pairs, the vapour pressure curve is a straight line. 

Here we have to expect, from the smallness of the heat change, that an equilibrium should be obtained even at low temperatures, and that, though it must be displaced in the direction of the formation of hydriodic acid, yet all the molecular species take part in the equilibrium with appreciable partial pressures. Experience confirms this fully. In addition to the examples mentioned, we may recall the formation of an ester, the classical case of chemical equilibrium since the formation of gaseous ethyl acetate and water from alcohol and acetic acid vapours takes place without any considerable heat change, an equilibrium must be produced just as with hydriodic acid, in which all the components participate in considerable concentrations since the vapour pressures of the four substances are not very different, this equilibrium must also be found for the liquid mixture. 

The surface tension of mixtures of water and ethyl alcohol at 25 C has been measured by Bircumshaw (J. Chem. Soc. 1922, 887). Partial vapour pressures of these laiixtures also at 25 C have been determined by Dobson (J. Chem. Soc. 1925, 2866). These values, smoothed in accordance with the requirements of the Duhem-Margules relation are given with related quantities at rounded mole fractions in table 1 (Guggenheim and Adam, Proc. Roy. Soc. A 1933, 139, 218). The subscript 1 relates to water and 2 to alcohol, x denotes mole fraction, p partial pressure, and y surface tension. 

Ternary mixtures are known where the mixture has a higher vapour pressure than any of its components, for example ethyl alcohol, chloroform and hexane isopropyl alcohol, ethyl acetate, and cyclohexane. In all probability the number of components may be still greater but no actual observations appear to have been recorded. 

Kahlenberg(eo) showed that if a cell HgO/rubber/ethyl alcohol was set up the alcohol diffuses into the water more rapidly than water into alcohol. At 15 C. the vapour pressures are 12 mm. for water and 32 mm. for alcohol, so that, with the permeability constants of Dewar in Table 119, one could predict the direction of diffusion actually observed by Kahlen-berg. As usual the permeation velocities bear no simple relationship to molecular size or mass, the large molecule, ethyl chloride, being transmitted ten times as fast as the smaller molecule, methyl chloride. The solubility of the diffusing substance in the membrane is one important factor 4n diffusion. Another must be the extent to which the mem-... 

With ethyl alcohol and water the deviation is considerable, and more recent and accurate observations have shown that a particular mixture exerts a maximum vapour pressure, but the experiments of Konowaloff are not sufficiently numerous to bring out this point. 

Mixtures of Benzene with Alcohols.—Benzene is much more easily obtained in quantity than hexane, and behaves in a somewhat similar manner. The lower alcohols are miscible with benzene in all proportions but while methyl, ethyl, isopropyl, w-propyl, tertiary butyl and isobutyl alcohols form mixtures of maximum vapour pressure with that hydrocarbon, isoamyl alcohol does not, and it is practically certain that no alcohol of higher boiling point would form such a mixture. 

Fig. 16. Effect of degree of crosslinking (% DVB) of standard (non-porous) ion exchanger on initial transesterification rate, r° (mol kg-1 h-1), of ethyl acetate with 1-propanol [436]. (1) Liquid phase at 52°C initial composition (mole%), 0.4 ethyl acetate, 0.4 1-propanol, 0.2 dioxan (solvent). (2) Vapour phase at 120°C partial pressure of reactants, 0.5 bar (ester—alcohol ratio 1 1).

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