Saturated vapour pressure calculations

Moisture precipitation Apart from wetting by sea-spray, moisture may either be deposited on a surface by rainfall or dew formation. For a known ambient humidity the dew point can be calculated, using the expression given previously, from standard tables giving the saturated vapour pressure of... 

The saturation vapour pressures are calculated as a function of temperature using the Antoine equation, equation 11.6, and the constants given in Example 11.3, and then, from Raoult s Law, Equation 11.1, the actual vapour pressures are given by ... 

There is no need to mention a condition if it does not affect the calculation. For example, there is no need to mention ambient pressure when defining saturated vapour pressure (SVP) as only temperature will alter the SVP of a volatile. 

If the saturation vapour pressure and molecular area of krypton at this temperature are 19.0 mmHg and 21 x lO-20 m2, respectively, calculate a specific surface area for the solid. 

P9 Density evaluated at 90% of the saturation (vapour) pressure at inlet temperature, T), after a flash calculation. For a multicomponent mixture, use the bubble point pressure at T). The flash calculation should preferably be carried out isentropically, but an isenthalpic flash is sufficient CO E D)... 

Most models to calculate the pore size distributions of mesoporous solids, are based on the Kelvin equation, based on Thomson s23 (later Lord Kelvin) thermodynamical statement that the equilibrium vapour pressure (p), over a concave meniscus of liquid, must be less than the saturation vapour pressure (p0) at the same temperature . This implies that a vapour will be able to condense to a liquid in the pore of a solid, even when the relative pressure is less than unity. This process is commonly called the capillary condensation. 

The direct determination of the saturation pressure of the adsorptive has the advantage of providing the real p° and, with nitrogen, of allowing one to calculate the adsorption temperature to the nearest 0.01 K. Since the surface layer of a cryogenic liquid tends to become colder (because of evaporation) than the lower part of the liquid (Nicolaon and Teichner, 1968), it is necessary to condense the adsorptive in the bottom of a double-walled ampoule, so that the location of the condensation is very close to the adsorbent sample. Measurement of the sample temperature by means of a resistance thermometer is more straightforward, but requires calibration against the saturation vapour pressure thermometer. 

The saturated vapour pressure of HF has been redetermined for the temperature range 273—303 K 167 this leads to a calculated boiling point of 292.90 K, at which temperature the association factor is estimated to be 3.75. Raman scattering by monomeric HF in the gaseous state and at low concentration in liquid SF6 has been studied by Le Duff and Holzer 168a Birnbaum has confirmed that rotational fine structure is evident in the far-i.r. spectrum in solution in SF6.1681 The Raman work also yielded some results on the HF polymer bands at 2900—3800 cm 1 these were said to be consistent with the presence of hexameric and tetrameric species.1680 The mean amplitudes of vibration of the cyclic hexamer (HF)6 have been calculated169 and the results compared with those from electron diffraction. 

Bakeeva, Pashinkin, Bakeev, and Buketov [73BAK/PAS] measured the selenium dioxide pressure over gold selenite in the interval 489 to 599 K by the dew point method. The pressure was calculated from the dew point temperature by the relationship for the saturated vapour pressure in [69SON/NOV]. The data in the deposited VlNITl document (No. 4959-72) have been recalculated with the relationship selected by the review. The enthalpy and entropy changes obtained from the temperature variation of the equilibrium constant are A //° ((V.123), 544 K) = (576.8 13.0) kJ-mol and A,S° ((V.123), 544 K) = (899.4 + 24.0) J-K -mor. The uncertainties are entered here as twice the standard deviations from the least-squares calculation. 

The vapour pressures obtained from dew point measurements will depend on the relationship used for the temperature dependence of the saturated vapour pressure. A number of relationships, = f (7), have been proposed for the equilibrium Se02(cr) Se02(g), see Section V.2.2.3. in Chapter V. In order to obtain consistency it is necessary to revise previous vapour pressures calculated from the dew point temperature, to conform with the accepted = f (7 ) function. The problem met in this revision has been the fact that in some instances only p values have been published, while the dew point temperatures and the relationship used to obtain are absent. 

Equation (1) is a useful route to calculating headspace concentrations above a pure substance from vapour pressures c is the gas phase concentration in g 1 1, p° is the saturated vapour pressure in mmHg, and T is the temperature in Kelvin. Equation (2) is the same equation restated in terms of concentration m in mol 1 1 at a temperature of 25 °C for cases where the molecular mass is unknown. These equations derive directly from the ideal gas equation. 

The available micropore volume Wa can be calculated from tlie dry micropore volume, W , the amount of pre-adsorbed water, Wpre, the amount of water ad- or desorbed by the contaminated air stream, AWair. and the amount of water replaced by the vapour AWg. The latter being function of the total amount of water on the carbon (Wpre + AWatr), the ratio of the amounts of water and vapour in the air stream ([C +C ]/Co) and the ratio of their saturation vapour pressures ([i s+Pflr]/ ). The value of Wo thus obtained can be used in the Dubinin-Radushkevich equation (see section 5.2.2) to calculate tlie capacity (We ) under humid conditions. 

Vapour Oversaturation One of the essential conditions for the CDV mechanism for reactions ending in the formation of solid products is the presence of oversaturated vapours of these products above the reactant surface. This becomes obvious when we compare the equilibrium vapour pressure Peq for the product species at the primary stage of the CDV reaction (disregarding the condensation stage) with the saturated vapour pressure Poo (A) for the solid product A. Table 2.2 illustrates this reasoning with the corresponding data calculated for some well-known decomposition reactions. This relation is apparently valid for the decomposition of any compound decomposed up to the solid product. 

RH = Mean relative humidity, calculated by using the saturation vapour pressure Ps at the measured temperature, and the value for Pd found in the previous column. 

A stoppered 2.0 dm flask was half-filled with water at exactly 40 °C. Calculate the number of water molecules in the water vapour. (The saturated vapour pressure of water at 40 °C is 7370 Pa.)... 

Here ns is the amount of substance of stationary liquid, pi is the saturated vapour pressure of the solute at temperature r. Bag is the mixture virial coefficient for solute 4- carrier gas interaction, Bcc is the virial coefficient of the carrier gas, Fjj is the partial molar volume of the solute at infinite dilution in the solvent, is the molar volume of pure liquid A, and pi and po are the column inlet and outlet pressures. The chemical potential at infinite dilution can be calculated by measuring the retention volume of an infinitely small sample for various inlet and outlet pressures and extrapolation to zero pressure drop across the column. Everett and Stoddart proposed using equation (33) to determine the mixture second virial coefficients. The precision in Bag from this method is nearly equivalent to the best static methods. The assumptions required to derive the above equation have been examined by a number of authors. - ... 

During this type of measurement, the volume of gas adsorbed by a unit mass of solid denoted by VyW depends on the equilibrium pressure, the absolute temperature, the solid, and the gas. The adsorbable gas will be below it s critical temperature and the pressure inside the equipment as measured by the manometer shown is expressed as a fraction of the saturation vapour pressure P. The resulting ratio P/P is called relative pressure. The amount of gas adsorbed can be calculated using the gas law relationships, the measured pressures, and known volumes of the equipment. 

Here, R is the gas constant, Mj is the solvent s molecular weight, and P 22 are the saturated vapour pressure and second virial coefficient of the pure solvent at temperature T, respectively. The required vapour pressures and virial coefficients can be calculated or estimated from known relationships [473-477]. Other treatments for the determination of y , which include a term to correct for the free volume contribution due to differences in the size of the solute and solvent, have also been used [478, 479]. The temperature dependence of the resulting solute activity coefficient is related to the infinite dilmion partial molar excess Gibbs energy (AG ) through Eq. (9). 

Boiling of a Uquid takes plcice at the temperature where the saturated vapour pressure of the corresponding gas phase increases the pressure in the ambient atmosphere. Calculate, based on thermodynamic standard values, the boiling point of water when the pressure in the ambient atmosphere is p = 2000 Pa ... 

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