Vapor pressure lowering definition

This relationship constitutes the basic definition of the activity. If the solution behaves ideally, a, =x, and Equation (18) define Raoult s law. Those four solution properties that we know as the colligative properties are all based on Equation (12) in each, solvent in solution is in equilibrium with pure solvent in another phase and has the same chemical potential in both phases. This can be solvent vapor in equilibrium with solvent in solution (as in vapor pressure lowering and boiling point elevation) or solvent in solution in equilibrium with pure, solid solvent (as in freezing point depression). Equation (12) also applies to osmotic equilibrium as shown in Figure 3.2. 

In this study, a thermodynamic framework has been presented for the calculation of vapor-liquid equilibria for binary solvents containing nonvolatile salts. From an appropriate definition of a pseudobinary system, infinite dilution activity coefficients for the salt-containing system may be estimated from a knowledge of vapor pressure lowering, salt-free infinite dilution activity coefficients, and a single system-dependent constant. Parameters for the Wilson equation may be determined from the infinite dilution activity coefficients. 

Suppo.se that a colligative property of the polymer solution is measured. These are properties that depend on the number of dissolved solute molecules and not on their sizes (see also Section 2.10). Osmotic pressure, vapor pressure lowering, and freezing point depression are some examples of colligative properties. If the value of the property measured is P, then by definition... 

The simplicity and generality of Equation 6.5-3 are surprising. According to the equation, if a solution contains 20 mole% solute, then the solvent partial pressure is 80% of the vapor pressure of pure solvent at the system temperature, regardless of the temperature, the pressure, and what the solute and solvent are. (Hence, vapor pressure lowering is a colligative property, by definition.) The only stipulations are that Raoult s law holds and the solute is nonvolatile, nonreactive, and nondissociative. 

Vapor pressure, which is the tendency of a liquid to release vapors to the surrounding area, goes down as MW increases but goes up as temperatures rise. By definition, the more volatile a liquid, the higher its vapor pressure and the lower its boiling point. Examples are ... 

Nonflammable indicates that no flash point was observed by the ASTM test method D-3278-82 or D-56 below the boiling point of the solvent mixture or below 100°F, whichever is lower (this is the DOT, ANSI, and NFPA definition). The composition of liquid blends can vary from the originally supplied composition during use, owing to tile differing vapor pressures of the individual constituents. Care must be taken to avoid preferential loss of PFCs, which would result in flammable mixtures. 

In addition to equilibrium between the liquid-phase water in the sample and the vapor phase, the internal moisture equilibrium of the sample is important. If a system is not at internal moisture equilibrium, one might measure a steady vapor pressure (over the period of measurement) that is not the true water activity of the system. An example of this might be a baked good or a multicomponent food. Initially out of the oven, a baked good is not at internal equilibrium the outer surface is at a lower water activity than the center of the baked good. One must wait a period of time in order for the water to migrate and the system to come to internal equilibrium. It is therefore important to remember the restriction of the definition of water activity to equilibrium. 

Since an azeotrope by definition has either a higher or a lower vapor pressure than that of any of the components, the azeotropic vapor pressure curve will always lie above or below the curves of the components. This is indicated schematically in Figure 1 where A and B are vapor pressure curves of the components and C is the vapor pressure of the azeotrope. If curve C crosses either A or B, the azeotropic vapor pressure is no longer greater or less than any of the components and the system will become nonazeotropic at the point of intersection. On the other hand, if the azeotropic curve is parallel to the other curves the system will be azeotropic up to the critical pressure. 

The 90% soln is a colorless liq. Prone to explode on contact with metals, their oxides, reducing substances, or on distillation. Has lower vapor pressure than formic acid. Miscible with water, ale, ether. Sol in benzene, chloroform. Solns are unstable, gassing being noticeable after a few hours, and the effective concn showing a definite decline in 2 hrs. 

Since an azeotrope by definition has either a higher or a lower vapor pressure than that of any of the components, the azeotropic vapor pressure curve will always lie above or below the curves of the components. This is indicated schematically in Figure 1 where A and B are vapor... 

In film deposition, the situation is often complicated by the fact that the vapor and the substrate are not phases of the same material, and by the fact that the temperature of the substrate is usually lower than that of the vapor. The definition of equilibrium vapor pressure is not so clear in this case. However, in most cases there will be some level of vapor pressure below which deposition of film material onto the growth surface will not occur this serves as an operational definition of Pe for film growth. 

The VAPOR PRESSURE of a liquid is the pressure exerted by the vapor that is in equilibrium with the liquid at a definite temperature. The vapor pressure depends on the temperature and on the nature of the liquid it is, within the limits of the ideal gas law, independent of the presence of other gases, Solids, too, exert vapor pressures, but they are usually lower than those of liquids. 

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