Vapor pressure of solvent

To review briefly, the osmotic pressure in a three-dimensional situation is that pressure required to raise the vapor pressure of solvent in a solution to that of pure solvent. Thus, remembering Eq. Ill-16,... 

VP = vapor pressure of solvent glc = ga.sliquidchromatography, SE = swelling equilibria Op = osmotic pressure. 

What are the consequences What is the maximum pressure Vapor pressure of solvent as a function of temperature Gas evolution Differential Thermal Analysis (DTA) / Differential Scanning Calorimetry (DSC) Dewar flask experiments... 

In this equation, Pt is the vapor pressure of solvent over the solution, P° is the vapor pressure of the pure solvent at the same temperature, and Xj is the mole fraction of solvent. Note that because Xj in a solution must be less than 1, P must be less than P°. This relationship is called Raoult s law Francois Raoult (1830-1901) carried out a large number of careful experiments on vapor pressures and freezing point lowering. 

Fig. 6.1. Vapor pressures of solvents as a function of temperature. 1 glycerin, 2 DMSO (C3Hg03), 3 water, 4 ethanol, 5 aceton.

Membrane distillation involves partially evaporating a solution through a microporous membrane that is vapor-permeable but liquid-repellent. The membrane has no permselectivity, but provides a stable liquid-gas-liquid interface for vapor transfer. As shown in Fig. 28, the membrane separates a heated feed solution from a cooler product solution. Since the vapor pressure of solvent in the feed solution is higher than that in the product solution, solvent... 

Historically, the most common method of drying of pharmaceutical powders has been tray-drying. With this method, wet powder or granulation is placed on paper-lined trays, usually solid or perforated metal, which are then placed directly onto racks in a drying chamber (oven) or onto movable racks, or trucks, that are wheeled into an oven. The heat and low relative vapor pressure of solvent provided by the flow of heated, dry air throughout the chamber provide a driving force for solvent transfer to and subsequent removal from the particle surfaces of the powder. This results in the gradual overall loss of solvent from the bulk powder. 

Osmosis tends to equalize the escaping tendencies of the solvent on both sides of the semipermeable membrane. Escaping tendency can be measured in terms of partial vapor pressure of solvent above the solution. 

Pure solid solvent coexists at equilibrium with its characteristic vapor pressure, determined by the temperature (Section 10.4). Solvent in solution likewise coexists with a certain vapor pressure of solvent. If solid solvent and the solvent in solution are to coexist, they must have the same vapor pressure. This means that the freezing temperature of a solution can be identified as the temperature at which the vapor-pressure curve of the pure solid solvent intersects that of the solution (Fig. 11.12). As solute is added to the solution, the vapor pressure of the solvent falls and the freezing point, the temperature at which the first crystals of pure solvent begin to appear, drops. The difference ATf = T/ — Tf is therefore negative, and a freezing-point depression is observed. 

FIGURE 11.12 The vapor pressure of solvent above a dilute solution, compared with that above pure liquid and solid solvent. The depression of the freezing point from Tf to T is shown. 

Using Flory-Huggins theory it is possible to account for the equilibrium thermodynamic properties of polymer solutions, particularly the fact that polymer solutions show major deviations from ideal solution behavior, as for example, the vapor pressure of solvent above a polymer solution invariably is very much lower than predicted from Raoult s law. The theory also accounts for the phase separation and fractionation behavior of polymer solutions, melting point depressions in crystalline polymers, and swelling of polymer networks. However, the theory is only able to predict general trends and fails to achieve precise agreement with experimental data. 

Equation (3.65), in which pilp° is the relative vapor pressure of solvent over solution, can be used for the determination of x- For a polymer of very high molecular weight, V1/V2 is small and may be neglected. Then Eq. (3.65) becomes simpler ... 

In a series of experiments, F. Raoult measured the vapor pressures of solvents and solutions with changing concentrations of solutes in them, and found that some ideal liquid solutions obey the following equation, named Raoult s law ... 

In quantitative terms, we find that the vapor pressure of solvent above the solution (Psoivent) cquals the mole fraction of solvent in the solution (Xsoivem) times the vapor pressure of the pure solvent (P°oivent)- This relationship is expressed by Raoult s law ... 

Raoult s law, calculating vapor pressure of solvent above a solution... 

Fig. 2.1-12 Vapor pressure of solvent and of solute vs. the temperature left) and the partial pressure vs. the mole fraction at a constant temperature right, Raoult-van t Hoff s law for...

The constants a and b are specific to each group of solvents. Figure 2.3.12 shows that estimation of flash point from vapor pressure of solvent is less aceurate than its estimation from boiling point. 

Raoult, F. M. 1887. General law of the vapor pressure of solvents. Comptes Rendus Hebdomadaires des Seances de VAcademie des Sciences. 104, 1430. 

At least three components are present in the absorption process the inert carrier gas, the solvent as an auxiliary substance, and the gas component i to be absorbed. Under steady-state operation, flow rates of the pure solvent Lj and the inert carrier gas Gj-are constant. The amount of solvent required assuming a low vapor pressure of solvent and neglecting solubility of the carrier gas in the solvent, follows from a mass balance over the absorber (see Fig. 3-4)... 

Figure 2.3.12. Flash point vs. vapor pressure of solvent.

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