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Equilibrium vapour pressure

The equilibrium vapour pressure, P, over a curved surface is defined by tlie Kelvin equation... [Pg.2761]

The normal melting point of a substance is the temperature at which solid and hquid are in equilibrium at atmospheric pressure. At the triple point, the pressure is the equilibrium vapour pressure of the system (solid liquid - vapour) and the temperature differs from the melting point. The difference is, however, quite small—usually only a fraction of a degree—since the line TV departs only slightly from the vertical within reasonable ranges of pressure. [Pg.38]

We may now understand the nature of the change which occurs when an anhydrous salt, say copper sulphate, is shaken with a wet organic solvent, such as benzene, at about 25°. The water will first combine to form the monohydrate in accordance with equation (i), and, provided suflScient anhydrous copper sulphate is employed, the effective concentration of water in the solvent is reduced to a value equivalent to about 1 mm. of ordinary water vapour. The complete removal of water is impossible indeed, the equilibrium vapour pressures of the least hydrated tem may be taken as a rough measure of the relative efficiencies of such drying agents. If the water present is more than sufficient to convert the anhydrous copper sulphate into the monohydrate, then reaction (i) will be followed by reaction (ii), i.e., the trihydrate will be formed the water vapour then remaining will be equivalent to about 6 mm. of ordinary water vapour. Thus the monohydrate is far less effective than the anhydrous compound for the removal of water. [Pg.41]

The technique is useful in that only small amounts of the sample polymer are needed, though experimentally it is time-consuming and may require great patience in use. This is because the technique does not measure equilibrium vapour-pressure lowering, but measures vapour-pressure lowering in a steady-state situation. Thus care must be taken to ensure that time of measurement and droplet size are standardised for both calibration and sample measurement. [Pg.83]

Magnesium sulphate is a useful drying agent as can be seen from the following table of equilibrium vapour pressures of the various possible tems at 25° ... [Pg.51]

Khan, L, Brimblecombe, P., and Clegg, S.L. Solubilities of p3mrvic acid and the lower (Ci-Cg) carboxylic acids. Experimental determination of equilibrium vapour pressures above pure aqueous and salt solutions, J. Atmos. Chem., 22(3) 285-302,1995. [Pg.1678]

The general field of measuring thermodynamic quantities using gas-phase methods is based simply on Eq. (3.55) where the activity of component i (Oj) is equal to the vapour pressure of i in the alloy divided by the equilibrium vapour pressure of pure i. [Pg.84]

The BET method (Brunauer, Emmett and Teller, 1938) with N2 as the adsorbate, is by far the most common method of measuring the surface areas of Fe oxides. Various commerical instruments are available for these measurements. The method involves measuring the extent of adsorption of N2 (at the boiling temperature of liquid N2 - 77 K) on the outgassed solid as a function of the relative pressure, p/po. he. the adsorption isotherm p is the partial pressure of the adsorbate and po is its equilibrium vapour pressure. The following linear relationship exists between the amount adsorbed, v, (cm g ) and the relative vapour pressure, p/po, ... [Pg.95]

If condensation of liquid in the micropores of charcoal when brought into contact with a vapour should occur the equilibrium vapour pressure above these constricted liquid filled capillaries will be much less than above a plane surface of liquid (see Chap. ix). Under these conditions the liquid filling the pores will be included in the amount of vapour adsorbed by the charcoal and give an erroneous impression as to the true extent of adsorption. At the same time for actual condensation to occur it is necessary that a mobile free surface of liquid should first be formed at some point in the capillary, in order that the surface forces of the liquid may promote further condensation. The primary formation of a layer more than one molecule thick is thus an essential preliminary to the process of capillary condensation. [Pg.132]

Figure 2.10 Schematic diagram showing that the equilibrium vapour pressure changes with the curvature of the liquid-vapour interface. Figure 2.10 Schematic diagram showing that the equilibrium vapour pressure changes with the curvature of the liquid-vapour interface.
Although saturated vapours can be reproduced precisely in the laboratory the application of equilibrium vapour pressures to the prediction of field volatilization rates are fraught with difficulties. The pesticide may interact with other spray components to change the physical characteristics of the deposits. As pointed out by Hartley (4) a pesticide which can exist in a supercooled state (eg. impure DDT in thin films) will be more volatile and more soluble than if it is crystalline. As a rough approximation a crystalline substance becomes one-third to one-fourth as volatile as the supercooled liquid for each... [Pg.213]

A solution is composed of benzene (B) and toluene (T). The Raoult s law holds for both benzene and toluene. The equilibrium vapour pressures of benzene and toluene are 102.4kPa and 39.0kPa, respectively, at 81°C. Calculate the mole fraction of benzene in the vapour which is in equilibrium with the NB = 0.5 solution. [Pg.83]

Using this equation AHV can be estimated with a knowledge of the equilibrium vapour pressure of a liquid at two different temperatures. For the solid-vapour phase boundary (sublimation), an analogous equation is obtained by replacing AHv with the heat of sublimation AHs. [Pg.140]

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. [Pg.38]

Silica gels were deuterated by pumping D20 at equilibrium vapour pressure over the sample. Time and temperature of both the adsorption and evacuation step were varied. The continuous flow of D20 vapour overcomes the need for repeating the procedure in several reaction cycles. The spectrum of silica gel, pretreated at 473 K under vacuum, before and after room temperature deuteration is shown in figure 3.5. Optimal exchange was observed if the adsorption was performed for 1 h at room temperature and the evacuation at the same temperature as pretreatment. [Pg.72]

If pure chlorine is to be liquefied at a constant temperature, it must be compressed to a pressure equalling the equilibrium vapour pressure of the liquid chlorine at the same temperature. The evolved condensation heat must be then lead away. If the chlorine is not entirely pure, compression must be increased by partial pressure of all inert gases. If chlorine containing other gases which cannot be liquefied readily is compressed it will be liquefied alone and its concentration in the gas phase will be decreased. Should further portions of chlorine be liquefied it would be necessary to increase the pressure in proportion to the increasing concentration of the inert gases in the gas phase. [Pg.297]

N.B. For organic vapours the solubility is normally expressed in weight per weight of polymer at equilibrium vapour pressure. In order to convert this into cm3(STP)/(cm3 bar) one has to multiply by the factor ... [Pg.659]

For a pure substance in condensed phase (solid or liquid) their vapour pressure is taken to be related to their activities. When we measure equilibrium vapour pressure, the vapour and the solid (or liquid) are at equilibrium and hence the activities of the constituent in both phases are the same. Hence, the activity of the vapour phase would represent the activity of the solid or liquid. [Pg.61]

Let us consider a pure substance say, water, at ambient conditions. Water naturally evaporates, and its equilibrium vapour pressure is equal to the pressure of vapour when water is kept in an evacuated chamber. Since equilibrium condition exists, free energy of transformation is zero or, stated differently, the free energies of the two phases are same. Since it is the case of a single pure substance, we say that the activities of the two phases are same. [Pg.62]

When two or more components mix to form a solution, naturally the properties of the individual constituents get affected. In the example of water-alcohol mixture, if absolute (100%) alcohol is diluted with water, the vapour pressure of alcohol decreases almost proportionally to the concentration of alcohol in the solution. On the other hand, the equilibrium vapour pressure of water starts increasing almost (but not exactly) proportionally to the concentration of water in the solution. The pressure exerted by the vapours of the solution is therefore made up of the partial pressures of alcohol and water. Thus, any property of the solution is made up of partial properties of the constituents in the solution, which we denote with a bar (-) on top. [Pg.62]


See other pages where Equilibrium vapour pressure is mentioned: [Pg.754]    [Pg.2761]    [Pg.41]    [Pg.112]    [Pg.100]    [Pg.342]    [Pg.888]    [Pg.15]    [Pg.215]    [Pg.100]    [Pg.342]    [Pg.21]    [Pg.325]    [Pg.107]    [Pg.145]    [Pg.54]    [Pg.41]    [Pg.218]    [Pg.221]    [Pg.221]    [Pg.93]    [Pg.419]   
See also in sourсe #XX -- [ Pg.126 ]

See also in sourсe #XX -- [ Pg.129 ]




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Equilibrium pressure

High-pressure vapour-liquid equilibria

Phase equilibria involving vapour pressure

Phase equilibria vapour pressure

Solution-vapour equilibrium constant pressure curves

The dependence of vapour -solution equilibria on temperature and pressure

Vapour pressure

Vapour-liquid equilibria at high pressures

Water vapour, equilibrium pressure

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