Liquids vapor pressure curve

Retrieve the vapor pressure and the liquid density data for methane from the DDBSP Explorer Version and export the values to Excel. Implement a liquid vapor pressure curve calculation for the van der Waals equation of state in Excel-VBA and compare the results along the vapor-liquid coexistence curve to the experimental data. 

Liquid helium-4 can exist in two different liquid phases liquid helium I, the normal liquid, and liquid helium II, the superfluid, since under certain conditions the latter fluid ac4s as if it had no viscosity. The phase transition between the two hquid phases is identified as the lambda line and where this transition intersects the vapor-pressure curve is designated as the lambda point. Thus, there is no triple point for this fluia as for other fluids. In fact, sohd helium can only exist under a pressure of 2.5 MPa or more. 

Figure 2. Determine the vapor pressure/critical pressure ratio by dividing the liquid vapor pressure at the valve inlet by the critical pressure of the liquid. Enter on the abscissa at the ratio just calculated and proceed vertically to intersect the curve. Move horizontally to the left and read r< on the ordinate (Reference 1).

The vapor pressure (P ) of a pure liquid at a given temperature (T) is the pressure exerted by its vapor in equilibrium with the liquid phase in a closed system. All liquids and solids exhibit unique vapor pressure-temperature curves. For instance, in Figure 2-79, lines BA and AC represent the equilibrium vapor pressure curves of the solid and liquid phases, respectively. 

Systems in which the saturated vapor pressure curve cuts a three-phase line of liquid + liquid + gas at a second quaternary point (solid + liquid + liquid + gas). Such systems have the first (or normal) quaternary point (solid + solid + liquid + gas) at lower temperatures and pressures (Fig. 13). Examples, ethane +... 

FIGURE 8.10 The liquid-vapor boundary curve is a plot of the vapor pressure of the liquid (in this case, water) as a function of temperature. The liquid and its vapor are in equilibrium at each point on the curve. At each point on the solid liquid boundary curve (for which the slope is slightly exaggerated), the solid and liquid are in equilibrium. 

An exceptional case of a very different type is provided by helium [15], for which the third law is valid despite the fact that He remains a liquid at 0 K. A phase diagram for helium is shown in Figure 11.5. In this case, in contrast to other substances, the solid-liquid equilibrium line at high pressures does not continue downward at low pressures until it meets the hquid-vapor pressure curve to intersect at a triple point. Rather, the sohd-hquid equilibrium line takes an unusual turn toward the horizontal as the temperature drops to near 2 K. This change is caused by a surprising... 

Pure CIF3O2 is colorless as a gas or liquid and white as a solid. Some of its measured (68) physical properties are summarized in Table XX. Near its melting point the vapor pressure above liquid CIF3O2 was found to be reproducibly lower than expected from the vapor pressure curve given in Table XX. This indicates that close to the melting point some ordering effect occurs in the liquid. 

Temperature at the critical point (end of the vapor pressure curve in phase diagram) is termed critical temperature. At temperatures above critical temperature, a substance cannot be liquefied, no matter how great the pressure. Pressure at the critical point is called critical pressure. It is the minimum pressure required to condense gas to liquid at the critical temperature. A substance is still a fluid above the critical point, neither a gas nor a liquid, and is referred to as a supercritical fluid. The critical temperature and pressure are expressed in this text in -C and atm, respectively. 

The Class I binary diagram is the simplest case (see Fig. 6a). The P—T diagram consists of a vapor—pressure curve (solid line) for each pure component, ending at the pure component critical point. The loci of critical points for the binary mixtures (shown by the dashed curve) are continuous from the critical point of component one, Ca , to the critical point of component two,Cp . Additional binary mixtures that exhibit Class I behavior are C02 -hexane and C02 benzene. More complicated behavior exists for other classes, including the appearance of upper critical solution temperature (UCST) lines, two-phase (liquid—liquid) immiscibility lines, and even three-phase (liquid—liquid—gas) immiscibility lines. More complete discussions are available (1,4,22). Additional simple binary system examples for Class III include C02—hexadecane and C02 H20 Class IV, C02 nitrobenzene Class V, ethane— -propanol and Class VI, H20— -butanol. 

On such a two-phase coexistence curve, the system has only a single degree of freedom, so that, for a given T, the pressure P is fixed, and vice versa. For example, if the temperature of a liquid-vapor system is chosen as T = 25°C, the corresponding P (read from the vapor-pressure curve) must be 23.8 Torr, as shown by the dotted line in Fig. 7.1. 

If the lid is removed, and the external surroundings have partial pressure Ph2o less than 23.8 Torr ( relative humidity < 100% ), then water will evaporate from the beaker into the surroundings until the beaker is empty, because only vapor is stable under these conditions. However, if the external surroundings have partial pressure Ph2o >23.8 Torr, water will condense from the surroundings to fill the beaker, because only liquid is stable under these conditions. Thus, the saturation vapor pressure ( 100% relative humidity ) corresponds to the unique concentration (partial pressure) of water vapor that can coexist at equilibrium in the atmosphere above liquid water at 25°C. Other (T, P) points on the vapor-pressure curve can be interpreted analogously. 

Vaporization Transition Clausius-Clapeyron Equation For the liquid-vapor coexistence line ( vapor-pressure curve ), the Clapeyron equation (7.29) becomes... 

Figure 7.3 provides a more complete picture of the H20 phase diagram in the range of pressures up to lOkbar. (For comparison, the pressure at the bottom of Earth s deepest oceans is about 0.5 kbar and that in planetary interiors ranges above 1 Mbar.) The region covered in Fig. 7.1 is the narrow sliver under the dotted line in the lower right comer, with the entire liquid-vapor coexistence curve visually indistinguishable from... 

Figure 7.1-5. Pressure-temperature diagram of the system propane/water [13]. a, Propane gas/water b, propane gas/propane hydrate c, propane liquid/water d, propane liquid/propane hydrate e, propane gas/ice f, hydrate curve g, vapor pressure curve of propane.

It is normal to assume that the vapor leaving the top of a tower is at its dew point. That is, it is at equilibrium with the liquid on the top tray of the tower. Unfortunately, this assumption falls apart if the tower is flooding and liquid is being entrained overhead from the column, with the vapor. However, assuming a normal, nonflooded condition, we will guess that the tower-top temperature is 140°F. Using the vapor-pressure curves provided in Fig. 9.1, we would calculate as follows ... 

Then, the vapor pressure curves of the two components are terminated by critical points which, in turn are connected by a continuous liquid-gas (L-G) critical line. For nonionic fluids, type I is only found for components with critical temperatures that are very close to one another—for example, neighboring compounds in homologous series. 

The following diagram shows a close-up view of part of the vapor-pressure curves for two pure liquids and a mixture of the two. Which curves represent pure liquids, and which represents the mixture ... 

KEY CONCEPT PROBLEM 11.17 The following phase diagram shows part of the vapor-pressure curves for a pure liquid (green curve) and a solution of the first liquid with a second volatile liquid (red curve). 

The Clapeyron equation is most often used to represent the relationship between the temperature dependence of a pure liquid s vapor pressure curve and its latent heat of vaporization. In this case, dPat/dT is the slope of the vapor pressure—temperature curve, A His the difference between the volume of the saturated vapor, H, and the saturated liquid, and AEFap is the latent heat of vaporization. Commonly, T) is small in comparison to V and the ideal gas law is assumed for the vapor phase. 

Pressure has a marked effect on the azeotropic composition and vapor-liquid equilibrium diagrams of alcohol-ketone systems (J). This is due to the fact that the slopes of the vapor pressure curves of alcohols are appreciably greater than for ketones it results in an unusually larger change in the relative boiling points of the components of an alcohol-ketone system with change in pressure. 

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