Saturation vapor pressure, definition

A heat of immersion may refer to the immersion of a clean solid surface, qs.imm. or to the immersion of a solid having an adsorbed film on the surface. If the immersion of this last is into liquid adsorbate, we then report qsv.imm if tbe adsorbed film is in equilibrium with the saturated vapor pressure of the adsorbate (i.e., the vapor pressure of the liquid adsorbate P ), we will write It follows from these definitions... 

Finally water removal capacity of reactant streams, especially air stream, withdraws definitively a part of the water from the cell module. These quantities could become very significant at high temperature, exceeding the water produced by electrochemical reaction. This happens because evaporation rate and saturated vapor pressure of water increase with temperature in a non-linear relationship [1],... 

Let the saturated vapor pressure be j> and the pressure exerted on the inside of the walls be pT, which is a function of the height of the point at which the pressure is considered. As will be shown later, there is some ambiguity as to the definition of pressure when the pressure across a strip of atomic dimension is considered. 

When a pure substance is at equilibrium with its vapor, its gas-phase partial pressure is equal by definition to its saturation vapor pressure, p°. The gas-phase molar saturation concentration, c° = p°/RT, of a compound is determined by its chemical structure and for water at atmospheric conditions is, on a mass basis, the order of a few g m 3 (Figure 17.1). 

Trfcan be calculated recognizing that by definition RH = Pw/P°(To) and that at the dew point Pu< = p iTd). The dependence of the saturation vapor pressure on temperature is given by the Clausius-Clapeyron equation (15.8). Integration between Tq, p° Tq) and Td, Pu, yields... 

In addition, due to the curvature of the interface, a deviation of the saturated vapor pressure exists. This deviation can be calculated from the definition and properties of the Gibbs free energy and leads to Kelvin equation (Dullien, 1992) ... 

Definition of Raoult s law The partial pressure p, of component i in the vapor phase is at an adjusted equilibrium proportional to the mole fraction Xj in the liquid phase. The saturated vapor pressure depends on the equilibrium temperature. 

A saturated aqueous solution in contact with an excess of a definite solid phase at a given temperature will maintain constant humidity in an enclosed space. Table 11.4 gives a number of salts suitable for this purpose. The aqueous tension (vapor pressure, in millimeters of Hg) of a solution at a given temperature is found by multiplying the decimal fraction of the humidity by the aqueous tension at 100 percent humidity for the specific temperature. For example, the aqueous tension of a saturated solution of NaCl at 20°C is 0.757 X 17.54 = 13.28 mmHg and at 80°C it is 0.764 X 355.1 = 271.3 mmHg. 

The spectra in Figure 11.4 were recorded from headspace vapor either at room temperature (TNT, PETN) or elevated temperature (about 50°C for RDX). For TNT this corresponds to a saturated headspace vapor pressure of less than 10 ppb. At these levels strong signal is observed with relatively weak signal from room air. Explosives compounds that have been detected by the MS detector with high sensitivity include TNT, ADNT, DNT, NT, TNB, DNB, DMNB, RDX, HMX, EGDN, NG, PETN, and TATP. (see Explosive Definitions, page 329). 

For a gas at temperature T and pressure P containing a single condensable vapor A with mole fraction y>A and vapor pressure pXiT), Raoult s law [j a/ = Pa( )1 provides the basis for a number of definitions. If Raoult s law is satisfied, the vapor is saturated (or equivalently, the gas is saturated with A) if VaP < Pa(T), the vapor is superheated. If A is saturated and either the temperature is decreased or the pressure is increased, A will begin to condense. If liquid A is in contact with a gas phase and the system is at equilibrium, the A vapor in the gas must be saturated. 

For a given temperature, equilibrium corresponds to a completely determined value of the pressure, which is the tension of saturated vapor at the given temperature the densities of the liquid and of the vapor have definite values called the density of saturated liquid and the density of saturated vapor at this temperature on the other hand, the mass of liquid and the mass of Vapor that the system includes are not determined we may impose upon these two masses all the variations that have their sum constant, equal to the total mass of the system. 

Definitions related to humidity, vapor pressure, saturation, and volume are as follows the most useful are absolute humidity, vapor pressure, and relative humidity. 

A column having a completely defined single feed, an overhead product, a bottoms product, a condenser, a reboiler, and a fixed column pressure has three degrees of freedom if the number of trays is variable (Section 5.2). The column model depicted in Figure 5.3 meets these definitions and is used here to describe the method. Note that the condenser in this model is a partial condenser, so that the distillate is a saturated vapor. With three degrees of freedom, the column requires three specifications to define its operation. Let the condenser duty, q the distillate composition, 7, and the bottoms composition, Xg, be specified. 

If a gas is collected over a volatile liquid, such as water, a correction is made for the amount of water vapor present with the gas. A gas collected over water is saturated with water vapor, which occupies the total gas volume and exerts a partial pressure. The partial pressure of the water vapor is a constant for each temperature and is independent of the nature or pressure of the confined gas. This definite value of the vapor pressure of water may be found tabulated as a function of temperature in handbooks or in... 

Aerosol particles in the atmosphere usually carry with them some moisture. The amount of water associated with the aerosol depends on the relative humidity. Increasing the relative humidity condenses more water onto the particles, until finally, when the vapor pressure of water exceeds the saturation point, a certain number of particles grows into fog or cloud droplets. Meterologists call these particles condensation nuclei, or simply nuclei. Fogs and clouds are treated as separate systems and are not included in the normal definition of the atmospheric aerosol, even though they represent an assembly of particles suspended in air and thus constitute an atmospheric colloid. The smoothness of the transition from an assembly of aerosol particles to one of cloud elements makes it difficult to define a boundary line between both colloids. Due to the overlap of size ranges of the particles in both systems, any division will be rather arbitrary. 

Relative humidity is dehned as the ratio of the partial pressure of the vapor to the vapor pressure of the liquid at the gas temperature. It is usually expressed on a percentage basis, so 100 percent humidity means saturated gas and 0 percent humidity means vapor-free gas. By definition... 

On Fig. 23.2 temperatures are plotted as abscissas and humidities as ordinates. Any point on the chart represents a definite mixture of air and water. The curved line marked 100 percent gives the humidity of saturated air as a function of air temperature. By using the vapor pressure of water, the coordinates of points on this line are found from Eq. (23.3). Any point above and to the left of the saturation line represents a mixture of saturated air and liquid water. This region is important only in checking fog formation. Any point below the saturation line represents undersaturated air, and a point on the temperature axis represents dry air. The curved lines between the saturation line and the temperature axis marked in even percents represent mixtures of air and water of definite percentage humidities. As shown by Eq. (23.5), linear interpolation between the saturation line and the temperature axis can be used to locate the lines of constant percentage humidity. 

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