Super-cooled liquid vapor pressure

Of primary environmental interest are the melting point, boiling point (the temperature at which the vapor pressure equals atmospheric pressure), and related vapor pressure at environmental temperatures. Chapters 1,2, and 3 discuss these properties. Also of interest is the super-cooled liquid vapor pressure, i.e., the vapor pressure which a solid substance would have if it were liquid at environmental temperatures. This vapor pressure, which is shown dashed in the figure, can be obtained by extrapolating the liquid s vapor pressure below the melting point. It cannot be measured directly. For example, naphthalene melts at 80°C, well above environmental temperatures. Its measured solid vapor pressure depends on the stability of the crystal structure of the pure substance, symmetrical molecules... 

Vapor Pressure of Super-Cooled Liquid, Psci A thermodynamic cycle relating transitions between the three phases and the related free energies can be dehned. 

The vapor pressure of the super-cooled liquid is shown to be significantly higher than that of the solid, which would be expected. Melting points are usually available in the literature, however, values for the entropy of fusion, AAf are not as common. Molar heats of vaporization, AH are more likely to be listed, for example, values for this parameter have been compiled for a number of chlorinated aromatic compounds and for aromatic hydrocarbons. For many compounds it has been shown that the entropy of fusion approximates 56 J mol K , and AS/R = 6.79. ... 

An approach similar to that used for vapor pressure provides a relation for estimating the solubility of the super-cooled liquid,... 

The vapor pressure (of the super-cooled liquid) of chlorinated dibenzodioxins also correlates with molar volume (cm mol ) ... 

Figure 6.27 Distribution of polynuclear aromatic hydrocarbons, (a), and PCB congeners, (b), between vapor and particle phases from an air sample taken in Chicago related to vapor pressure of the super cooled liquid. [Reproduced with permission from W. E. Cotham and T. F. Bidleman, Environ. Set Technol. 29, 2782 (1995). Copyright 1995, American Chemical Society.]...

If a vapor is cooled rapidly, its vapor pressure will be larger than the saturation vapor pressure at this cold temperature, so that it becomes super-saturated. Under these conditions, condensation to the liquid state cannot occur spontaneously unless some nucleation... 

A gas in this context is referred to as saturated or 100% relative humidity, when the vapor pressure of water in the air is at the equilibrium with vapor pressure due to (liquid) water water (or ice, if cool enough) will fail to lose mass through evaporation when exposed to saturated air. Because the amount of water vapor in air is small, relative humidity, the ratio of the partial pressure due to the water vapor to the saturated partial vapor pressure, is much more useful. Water vapor pressure above 100% relative humidity is called super-saturated and can occur if air is rapidly cooled, for example, by rising suddenly in an updraft. 

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