Saturation Vapour Pressure Curve

Saturated vapour pressure curves ds A and B, where A (e.g. ethanol, more volatile than B (e.g. water. 

When the (P,T) state lies above flie saturation vapour pressure curve ABC, and to the right hand side of flie To isotherm. This is a stable superheated state . 

Let us consider the P-T diagram in Fig. 8.1, where XY is the saturation vapour pressure-temperature line, or alternatively the pressure versus boiling point curve. In addition to showing the saturation vapour pressure curve, the diagram can also be regarded as a thermodynamic state diagram, with the curve separating liquid and vapour phase thermodynamic states. 

During a transfer operation, the liquid state can cross the saturation vapour pressure curve XY resulting in the creation of two phases by two separable paths, or by combinations of the two paths, i.e.,... 

To prevent the occurrence of 2-phase flow during a hquid transfer, the change in thermodynamic states represented by both paths AB and AC must not end on, or cross, the saturation vapour pressure curve XY. 

Of course, the vapour pressure is very temperature dependent, and reaches P° = 101.325 kPa at the normal boiling point, Tb. The isochoric thermal pressure coefficient, dp/dT)v = otp/KT, can be obtained from the two quantities on the right hand side listed in Table 3.1. Except at T it does not equal the coefficient along the saturation line, (dp/dT)a, which is the normal vapour pressure curve. The latter temperature dependence is often described by means of the Antoine equation ... 

One consequence of this raising of vapour pressure is the well-known fact that water vapour will not condense in a dust-free (and ion-free) atmosphere, unless its vapour pressure considerably exceeds the saturation point. An 11 per cent, increase of vapour pressure would be required for condensation to drops of 10 6 cm. diameter when it is considered that a sphere this size contains about 140,000 water molecules, it is clear that the chance of so many coming together as to start drops of this size, or larger, is small some nucleus providing a less curved surface must be present if condensation is to occur anywhere near the usual saturated vapour pressure. 

Fig. 4 did, on the left of EiD to ice, right of that to water. Di corresponds to the pressure of pure water at the freezing point, and consequently lies above a m, which refers to the saturated solution also lies in the continuation of the curve OAj, since that, like a d, gives the pressure of ice from T)- to the right lies the vapour pressure curve for water. Further, the boundary between water and ice, DjEi, may be drawn from Dj upwards, and from A the line A a of cryohydric pressure, which is given on the horizontal plane by a line corresponding to the composition of the cryohydric solutions for difierent pressures. The new areas, given only by the projection, relate to conditions not previously taken into account ... 

Eq.(32) gives the relationship between the saturated vapour pressure of liquid over the curved (inside the pores) and the flat liquid surface, p and po, respectively, rj is the radius of the liquid meniscus, 7 is the surface tension of liquid, Vj is the molar volume and T is absolute temperature. It follows from Eq.(32) that the sharp emptying of the pore... 

It will be observed that at the transition temperature the vapour pressures are identical In the above case we meet with the pecukanty that the vapour pressure over the saturated solution actually decreases in the neighbourhood of the transition temperature, 1 e the vapour pressure curve becomes retroflex This is due to a large increase in solubility of the hexahydrate near its transition temperature, a great solubility necessarily depressing the vapour pressure Naturally, no such effect is observed in the case of the solid salts... 

The vapour pressure of the different systems of sodium sulphate and water can best be studied with the help of the diagram in Fig. 75, The curve ABCD represents the vapour-pressure curve of the saturated solution of anhydrous sodium sulphate. GC is the pressure cuiwe of decahydrate -f- anhydrous salt, which, as we have seen, cuts the curve ABCD at the quadruple point, 32 6°. Since at this point the solution is saturated with respect to both the anhydrous salt and the deca-... 

With regard to sodium sulphate heptahydrate, the same considerations will hold as in the case of the decahydrate. Since at 24 the four phases heptahydrate, anhydrous salt, solution, vapour can coexist, the vapour-pressure curves of the systems hydrate—anhydrous salt— vapour (curve EB) and hydrate—solution— vapour (curve FB) must cut the pressure curve of the saturated solution of the anhydrous salt at the above temperature, as represented in Fig. 75 by the point B. This constitutes, therefore, a second quadruple point, which is, however, metastable. 

Corresponding to the point Q/the melting-point of pure iodine, there is the point C, which represents the vapour pressure of iodine at its melting-point. At this point three curves cut i, the sublimation curve of iodine 2, the vaporisation curve of fused iodine 3, CiB, the vapour-pressure curve of the saturated solutions in equilibrium with solid iodine. Starting, therefore, with the system solid iodine— liquid iodine, addition of chlorine will cause the temperature of equilibrium to fall continuously, while the vapour pressure will first increase, pass through a maximum and then fall continuously until the eutectic point, B (Bjl), is reached. At this point the system is invariant, and the pressure will therefore remain constant until all the iodine has disappeared. As the concentration of the chlorine increases in the manner represented by the curve B/H, the pressure of the vapour also increases as represented by the curve Bj/iHi. At the eutectic point for iodine monochloride and iodine trichloride, the pressure again remains constant until all the monochloridc has disappeared. As the concentration of the solution passes along the curve HF, the pressure... 

Vapour Pressure. Quintuple Point.—In the case of Glauber s salt, we saw that at a certain temperature the vapour pressure curve of the hydrated salt cuts that of the saturated solution of anhydrous sodium sulphate. That point, it will be remembered, is a quadruple point at which the four phases sodium sulphate decahydrate, anhydrous sodium sulphate, solution, and vapour, can coexist and is also the point of intersection of the curves for four univariant systems. In the case of the formation of double salts, similar relationships are met with and also certain differences, due to the fact that we are now dealing with systems of three components. Two cases will be chosen here for brief description, one in which formation, the other in which decomposition of the double salt occurs with rise of temperature. 

DEN/SAF] Denisova, N. D., Safronov, E. K., Pustilnik, A. I., Bystrova, 0. N., Boundary liquid - vapour curve and saturated vapour pressure of zirconium and hafnium tetrachlorides, Russ. J. Phys. Chem., 41, (1967), 30-33. Cited on page 170. 

For type 4a the three-phase line LGSn runs through a pressure maximum between the triple point of the pure component II and the quadrupole point Q where a liquid and a gaseous phase coexist with the pure solid components I and II. This curve represents the vapour pressure curve above a solution saturated with solid component II it can be determined quite easily by experiment in a closed autoclave filled with component I and an excess of solid component II and has been found for aqueous solutions of NaCl, boric acid, borates, borax, etc. ... 

Fig. 9.3. Water vapour pressure curves for water vapour in moist air. The curves for the various relative humidities were calculated from the interpolated data of the saturation curve (100 %). Dew point temperature (e.g. 12 °C) for certain ambient temperature (e.g. 20 °C) and certain humidity (e g. 60 %) can be read from the graph by moving from the respective point on the 60-%-cuive to the saturation curve. The arrows indicate the reading steps...

Here, the region to the right of the vapour pressure curve represents the gaseous state. To the left side of the curve, the substance is liquid or solid. In the condition described by the curve liquid and saturated vapour coexist in equilibrium. When the temperature of an unsaturated (superheated) vapour is reduced, condensation starts at the saturation temperature (dew point temperature) corresponding to the actual vapour pressure. 

Figure 6.5 shows the vapour pressure (partial pressure) and the vapour concentration as a function ofthe liquid temperature of a flammable liquid [10]. The range D in Figure 6.5 shows the saturated vapour range. A saturated vapour exists only for a limited time. According to the vapour pressure, the vapour concentration descends to a concentration belonging to the liquid temperature. That is caused by condensation. In addition, the explosion Hmits, explosion points as well as the flash point are given in Figure 6.5. [7]. The LEL/UEL of a flammable liquid is the temperature related to the atmospheric pressure (1013 mbar) at which, under predefined test conditions, the concentration of the saturated vapour/air smixture above the liquid surface reaches the LEL/UEL. Therewith, the Lower Explosion Point (LEP) determines the lower limit temperature for the formation of explosive mixtures. If the vapour pressure curve and, for example the explosion limits of a pure liquid are known, the explosion points also can be assessed.

P-T diagram showing saturation vapour pressure versus temperature curve, separating liquid and vapour... 

Fig. 6.2 Equilibrium saturation vapour pressures of H2O and HNO3 ovta- solid (solid curves) and liquid (broken curves) H2O-HNO3 mixtures with HNO3 mass fractions of 0.5 and 0.0 (pure H2O). Also shown are partial pressures for H2O and HNO3 as observed in the background atmosphere around 17 km altitude [29]. Condensation temperatures for liquid mixture (points A and B) and solid (points C and D) mixtures are about 188 and 211 K respectively. For liquid and solid H2O (f2 = 0.0) condensation temperatures are about 179 and 191 K respectively...

The liquid solvent is in equilibrium with its vapour alone along the saturation curve (denoted by subscript a), but when an external pressure is imposed, the liquid boils only when its vapour pressure equals the external pressure. The normal boiling point, 7 b, is reached at standard atmospheric pressure,... 

Van Wijk and Seeder s viscosity equation, 91 vapour, density of saturated, 324 specific heat of saturated, 336, 346-7, 359 vapour pressure 226 alignment chart, 271 of aliphatic esters, 286 of alkali halides, 237,243 of benzene, 267 boiling-point method for, 235 in capillary tubes, 367 of carbon, 246 centri fugal force, effect of, on 292 constant, 335, 341 over curved surface, 366 determination of, 227-47 dew-point method, 241 of dibasic acids, 243 dynamical method, 235 effusion method, 241. electrification, effect of on, 238, 375 of elements 257 of esters, 250 f., 286 of fusible metal, 230 in... 

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