Toluene partial vapor pressure

A hypothetical solution of a solute B in a solvent A that obeys Raoult s law throughout the composition range from pure A to pure B is called an ideal solution. The law is most reliable when the components of a mixture have similar molecular shapes and are held together in the liquid by similar types and strengths of intermolecular forces. An example is a mixture of two structurally similar hydrocarbons. A mixture of benzene and methylbenzene (toluene) is a good approximation to an ideal solution, for the partial vapor pressure of each component satisfies Raoult s law reasonably well throughout the composition range from pure benzene to pure methylbenzene (Fig. 3.24). 

Figure 6.1 The Partial Vapor Pressures of Benzene and Toluene in a Solution at 80°C. Drawn from data of M. A. Rosanoff, C. W. Bacon, and R W. Schulze, J. Am. Chem. Soc., 36, 1993 (1914).

Substances with similar molecules usually form nearly ideal solutions. Toluene and benzene are an example. Figure 6.1 shows the partial vapor pressures of benzene and toluene and the total vapor pressure in a solution at 80 C, plotted as functions of the mole fraction of benzene. The line segments in the figure correspond to Raoult s law, which is very nearly obeyed. 

The vapor pressure of pure benzene (component 1) at 20.0°C is eqnal to 74.9 torr, and that of pure toluene at this temperature is 21.6 torr. Assuming ideality, find the partial vapor pressure of each component, the total vapor pressure, and the mole fractions in the vapor at equilibrium with the solution of Example 6.2. 

We are being asked to find the mole fraction of benzene and of toluene in the vapor. From Example 14-6 we know the vapor pressure of pure benzene and pme toluene. We have already calculated the partial vapor pressures now we need to apply the definition of mole fraction. 

Colorless gas pungent suffocating odor density 2.975 g/L fumes in moist air liquefies at -101°C sohdifies at -126.8° vapor pressure at -128°C is 57.8 torr critical temperature -12.2°C critical pressure 49.15 atm critical volume 115 cm3/mol soluble in water with partial hydrolysis solubdity in water at 0°C 332 g/lOOg also soluble in benzene, toluene, hexane, chloroform and methylene chloride soluble in anhydrous concentrated sulfuric acid. 

Kinetics. Kinetic measurements were made by following CO uptake at constant pressure using the apparatus and procedure described earlier (17). The Ru catalyst concentration used was in the range (0.6-6.0) X 10 2A/. Total pressures up to 1 atm and CO partial pressures from 55-590 mm were used. The CO solubility in pure piperidine was 6.5 X 10"3M atm 1 at 21 °C and 5.8 X 10 3M atm 1 at 75°C, Henry s law being obeyed at least up to 1 atm the solubility in toluene was similar (5.7 X 10"3M atm"1 at both 21° and 75°C). The solubility in a toluene-piperidine mixture (1 1 by vol), 5.5 X 10"3Af atm 1 at 75°C was only slightly less than those in the pure solvents. The vapor pressures of piperidine and toluene differ by only about 15-20 mm between 50°-75°C, that of piperidine being the greater (18). Vapor pressure measurements on the solvent mixtures showed that Raoult s Law was obeyed approximately, and the partial CO pressures over toluene-piperidine solutions could be readily estimated. For practical purposes, the partial pressure of piperidine-toluene mixtures, 2.0-10.1M (neat) in piperidine could be taken as that of pure piperidine. 

Fig. 19 Polymer volume fraction (j) = h( iy //jsw in swollen films of two PS-h-PB diblock copolymers (.S //47 (circles) and SB10 (squares)) that have been equilibrated at p/po 50% of the partial chloroform (non-selective solvent) vapor pressure [114], and of SV films (triangles) equilibrated under p/po = 80% of toluene (selective solvent) [119] versus the number of layers (film thickness normalized by the respective structure dimension in bulk)...

Fig. 39. Fracture toughness Ki versus crack velocity in several partial toluene vapor pressures. O in air 0.5% mixture 0> 5% mixture the toughness is almost vapor pressure independent. From Ref., by permission of the publishers, Butterworth and Co. Ltd.

Problem Mixtures of benzene and toluene behave almost ideally at 30 C, the vapor pressure of pure benzene is 118.2 mm. and that of pure toluene is 36.7 mm. Determine the partial pressures and weight composition of the vapor in equilibrium with a liquid mixture consisting of equal weights of the two constituents. 

FIGURE 12.8 The dependence of the partial pressures of benzene and toluene on their mole fractions in a benzene-toluene solution fX c /uene I X en enei 80°C. This solution is said to be ideal because the vapor pressures obey Raoult s law. 

Equation 11.1-5 provides the starting point for the solution of this problem. Since the partial pressure of carbon dioxide and the vapor pressures of toluene and carbon disulfide are so low, the total pressure must be low, and we can assume, that... 

The diffusivity of toluene in air was determined experimentally by allowing liquid toluene to vaporize isothermally into air from a partially filled vertical tube 3 mm in diameter. At a temperature of 39.4°C, it took 96 x iff sec for the level of the toluene to drop from 1.9 cm below the top of the open tube to a level of 7.9 cm below the top. The density of toluene is 0.852 gm/cm , and the vapor pressure is 57.3 torr at 39.4°C. The barometer reading was 1 atm. Calculate the diffusivity and compare it with the value predicted from (16-3). Neglect the counterdiffusion of air. 

Figure 14.11 shows the vapor pressure versus mole fraction of benzene for the benzene-toluene system, which behaves ideally to a good degree of accuracy over the entire range of composition. The partial pressures of benzene and toluene, also shown in the figure, are linear functions of the mole fraction of benzene, since Raoult s law is obeyed. 

Vapor permeation of membrane-supported films of IZn has also been studied [31]. Examined as permeants were benzene, toluene, 4-picoUne, 2-picoline, cyclohexane, and methylcyclohexane. In pair-wise comparisons modest permeation selectivities were observed (i.e., factors of 1.1 to 9, depending on the permeant pairs compared). The competitive transport measurements were made at equal vapor pressures for the component pairs. The selectivities decrease if comparisons are made at equal reduced vapor pressures, P/Po, where Po is the vapor pressure at saturation. Nonspecific sorption of volatile compoimds at a given partial pressure generally inversely correlates with values for the saturated vapor pressure. 

Consider a mixture of 1.0 mol of benzene (CgHg) and 2.0 mol of toluene (C7Hg) (Afcen 0.33, Xtoi = 0.67). At 20 "C the vapor pressures of the pure substances are Pben = 75 torr and P(q1 = 22 torr. Thus, the partial pressures above the solution are... 

Strategy Assuming that the mixture of benzene and toluene is an ideal solution, the partial pressures of both benzene and toluene can be calculated using Raoult s law (Equation 9.8). To do this we need to convert grams of both benzene and toluene to moles and then determine the mole fractions, (a) The total vapor pressure is then obtained by adding together the partial pressures of benzene and toluene, (b) The mole fractions of benzene and toluene in the vapor phase can be determined from the partial pressures using Dalton s law. 

Using Raoult s law and the vapor pressures of pure benzene and toluene, the partial pressure of each component can be calculated as follows ... 

Let s examine this effect in a solution that contains equal amounts (mol) of benzene (CgHg) and toluene (C7H8) Xben = - toi = 0.500. At 25°C, the vapor pressure of pure benzene (Fben) is 95.1 torr and that of pure toluene (Pfoi) is 28.4 torr note that benzene is more volatile than toluene. We find the partial pressures from Raoult s law ... 

Toluene and benzene form liquid mixtures that are practically ideal and closely obey Raoult s law for partial pressure. For the binary system of these components, we can use the vapor pressures of the pure liquids to generate the liquidus and vaporus curves of the pressure-composition and temperature-composition phase diagram. The results are shown... 

CHECK The units of the answer (torr) are correct. The magnitude seems reasonable given the partial pressures of the pure substances. FOR PRACTICE 12.7 A solution of benzene (C5H5) and toluene (Cyllg) is 25.0% benzene by mass. The vapor pressures of pure benzene and pure toluene at 25 °C are 94.2 torr and 28.4 torr, respectively. Assuming ideal behavior, calculate the following (a) The vapor pressure of each of the solution components in the mixture. (b) The total pressure above the solution. (c) The composition of the vapor in mass percent. Why is the composition of the vapor different from the composition of the solution ... 

The vapor pressures of pure benzene and pure toluene at 25 °C are 95.1 and 28.4 mmHg, respectively. A solution is prepared in which the mole fractions of benzene and toluene are both 0.500. What are the partial pressures of the benzene and toluene above this solution What is the total vapor pressure ... 

Example 8 Calculation of Rate-Based Distillation The separation of 655 lb mol/h of a bubble-point mixture of 16 mol % toluene, 9.5 mol % methanol, 53.3 mol % styrene, and 21.2 mol % ethylbenzene is to be earned out in a 9.84-ft diameter sieve-tray column having 40 sieve trays with 2-inch high weirs and on 24-inch tray spacing. The column is equipped with a total condenser and a partial reboiler. The feed wiU enter the column on the 21st tray from the top, where the column pressure will be 93 kPa, The bottom-tray pressure is 101 kPa and the top-tray pressure is 86 kPa. The distillate rate wiU be set at 167 lb mol/h in an attempt to obtain a sharp separation between toluene-methanol, which will tend to accumulate in the distillate, and styrene and ethylbenzene. A reflux ratio of 4.8 wiU be used. Plug flow of vapor and complete mixing of liquid wiU be assumed on each tray. K values will be computed from the UNIFAC activity-coefficient method and the Chan-Fair correlation will be used to estimate mass-transfer coefficients. Predict, with a rate-based model, the separation that will be achieved and back-calciilate from the computed tray compositions, the component vapor-phase Miirphree-tray efficiencies. 

Although in the case of methylene chloride under normal pressure more than one-half of the gas phase consists of solvent vapor (57%), in the case of toluene and water this share amounts to only ca. 3-4% of the total pressure. In order to compare activities in various solvents at the same hydrogen pressure above the reaction solution, besides a different gas solubility for the solvents (i.e., the hydrogen concentration in solution), a different partial pressure of hydrogen must be taken into account. 

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