Henry’s Law references

When the ideally dilute solution is used as the reference for real solutions, thermodynamic properties are designated by (HL) for Henry s law reference. This reference is always used when some components are not liquids at the temperatures employed and may also be used if they are all liquids, but only very dilute solutions are being considered. For this reference, we treat the solvent in the same manner as for the (RL) reference ... 

Example 2. Using Fig. 2, what is the Henry s law constant treating acetone as the solute and what is the Henry s law constant treating chloroform as the solute Calculate Henry s law reference activity coefficients for both of these cases. 

A sample calculation of the Henry s law reference activity coefficients is... 

The Henry s law reference activity coefficients are plotted in Fig. 4. Note that this system shows positive deviation with respect to the ideally dilute behavior of Henry s law. 

If the solute is a solid, we will usually want to use a molality-based Henry s law reference, with aB = yBm. Equation (15) of Chapter 8 then becomes... 

At 30°C the vapor pressure of CS2 is 430 mm Hg. A solution of CS2 in acetone with xc 2 = 0.040 at this temperature is in equilibrium with a partial pressure of CS2 of 80 mm Hg. This solution can he considered ideally dilute. The partial pressure of CS2 over an equimolar solution of CS2 and acetone is 330 torr. Calculate yCS2 for the equimolar solution, using both the Raoult s law and Henry s law reference states. 

In the unsymmetric standard state convention, where the solvent is referenced to its pure state (Raoult s law reference state) and the solutes to the infinite dilution state (Henry s law reference state), the standard partial molar volume is equal to the pressure derivative of the chemical potential at... 

State the molecular conditions when a liquid or solid forms an ideal solution. Identify Lewis/Randall and Henry s law reference states for ideal solutions, including the molecular interactions on which each reference state is based. 

In this text, we use explicitly use the superscript Henry s to denote the Henry s law reference state. When the activity coefBcient does not have a superscript, we implicitly assume the Lewis/Randall reference state, although, in some cases, the expression may apply to both the Lewis/Randall reference state and the Henry s law reference state. 

Inspection of this expression shows that we can relate the activity coefficient in the Henry s law reference state to the activity coefficient in the Lewis/Randall reference state by ... 

To use the Henry s law reference state at high pressures, we need to correct for the pressure dependence of the Henry s law constant just as we did for the pure species fugacity above. Moreover, since the Henry s law constant is a function of the unlike species in the mixture, we have to obtain its experimental value for the specific species in the mixture. Values reported in the literature may be at a different temperature than the system of interest. In this section, we develop relationships for the pressure and temperature dependence of the Henry s law constant. 

The Henry s law reference state can be conceptualized as a hypothetical, pure fluid in which the characteristic energy of interaction is that between molecule i and the other molecules, that is, the i-j interactions ... 

Applying the Henry s law reference state for species i gives ... 

Since the defects are very dilute and are not defined in the Lewis/RandaU limit, we choose a Henry s law reference state for them, i.e., /zn = Wzn and Jv = This state is the hypothetical pure species characterized by all a b interactions its properties are given by those at infinite dilution. Thus, we use the partial molar Gibbs energy at infinite dilution for these terms in the Gibbs energy of reaction. 

Hydrogen Chloride—Water System. Hydrogen chloride is highly soluble in water and this aqueous solution does not obey Henry s law at ah concentrations. Solubhity data are summarized in Table 5. The relationship between the pressure and vapor composition of unsaturated aqueous hydrochloric acid solutions is given in Reference 12. The vapor—Hquid equiHbria for the water—hydrogen chloride system at pressures up to 1632 kPa and at temperatures ranging from —10 to +70° C are documented in Reference 13. 

Ideal gas properties and other useful thermal properties of propylene are reported iu Table 2. Experimental solubiUty data may be found iu References 18 and 19. Extensive data on propylene solubiUty iu water are available (20). Vapor—Hquid—equiUbrium (VLE) data for propylene are given iu References 21—35 and correlations of VLE data are discussed iu References 36—42. Henry s law constants are given iu References 43—46. Equations for the transport properties of propylene are given iu Table 3. 

Under equiUbrium or near-equiUbrium conditions, the distribution of volatile species between gas and water phases can be described in terms of Henry s law. The rate of transfer of a compound across the water-gas phase boundary can be characterized by a mass-transfer coefficient and the activity gradient at the air—water interface. In addition, these substance-specific coefficients depend on the turbulence, interfacial area, and other conditions of the aquatic systems. They may be related to the exchange constant of oxygen as a reference substance for a system-independent parameter reaeration coefficients are often known for individual rivers and lakes. 

For quite a number of gases, Henry s law holds very well when the partial pressure of the solute is less than about 100 kPa (I atm). For partial pressures of the solute gas greater than 100 kPa, H seldom is independent of the partial pressure of the solute gas, and a given value of H can be used over only a narrow range of partial pressures. There is a strongly nonlinear variation of Heniy s-law constants with temperature as discussed by Schulze and Prausnitz [2nd. Eng. Chem. Fun-dam., 20,175 (1981)]. Consultation of this reference is recommended before considering temperature extrapolations of Henry s-law data. 

Method of Moments The first step in the analysis of chromatographic systems is often a characterization of the column response to sm l pulse injections of a solute under trace conditions in the Henry s law limit. For such conditions, the statistical moments of the response peak are used to characterize the chromatographic behavior. Such an approach is generally preferable to other descriptions of peak properties which are specific to Gaussian behavior, since the statisfical moments are directly correlated to eqmlibrium and dispersion parameters. Useful references are Schneider and Smith [AJChP J., 14, 762 (1968)], Suzuki and Smith [Chem. Eng. ScL, 26, 221 (1971)], and Carbonell et al. [Chem. Eng. Sci., 9, 115 (1975) 16, 221 (1978)]. 

Referring to Figure 8-2, Henry s Law would usually be expected to apply on the vaporization curve for about the first 1 in. of length, starting with zero, because this is the dilute end, while Raoult s Law applies to the upper end of the curve. 

An existing lO-in. I.D. packed tower using 1-inch Berl saddles is to absorb a vent gas in water at 85°F. Laboratory data show the Henry s Law expression for solubility to be y = 1.5x, where y is the equilibrium mol fraction of the gas over water at compositions of x mol fraction of gas dissolved in the liquid phase. Past experience indicates that the Hog for air-water system will be acceptable. The conditions are (refer to Figure 9-68). 

M. Amon and C. D. Denson [33-34] attempted a theoretical and experimental examination of molding a thin plate from foamed thermoplastic. In the first part of the series [33] the authors examined bubble growth, and in the second [34] — used the obtained data to describe how the thin plate could be molded with reference to the complex situation characterized in our third note. Here, we are primarily interested in the model of bubble growth per se, and, of course, the appropriate simplification proposals [33]. Besides the conditions usual for such situations ideal gets, adherence to Henry s law, negligible mass of gas as compared to mass of liquid, absence of inertia, small Reynolds numbers, incompressibility of liquid, the authors postulated [33] several things that require discussion ... 

The reason for choosing a Henry s Law standard state can be seen by referring to Figure 6.13, which compares the Henry s law and Raoult s law standard states for CC14 in. yKC H O +. V2CCI4). At high, y2, Raoult s law... 

Here Ac = Ca - XhCw with Cg and Cw representing the concentrations in the air and water respectively and Kh the Henry s law constant. The parameter K, linking the flux and the concentration difference, has the dimension of a velocity. It is often referred to as the transfer (or piston) velocity. The reciprocal of the transfer velocity corresponds to a resistance to transfer across the surface. The total resistance R — K ) can be viewed as the sum of an air resistance (i a) and a water resistance (Rw). ... 

When solubility and vapor pressure are both low in magnitude and thus difficult to measure, it is preferable to measure the air-water partition coefficient or Henry s law constant directly. It is noteworthy that atmospheric chemists frequently use Kwa, the ratio of water-to-air concentrations. This may also be referred to as the Henry s law constant. 

If we take the standard state as the hypothetical 1 molar Henry s law solution (sometimes shortened to hypothetical ideal 1 molar solution, where the ideality referred to is Henry s law ideality in molarity units, that is, the proportionality of partial pressure and molarity, not Raoult s law ideality) we get... 

Experimentally jB is found to be finite. The slope of the relative adsorption versus composition, which is also finite, is referred to as Henry s law for surfaces. For electronegative elements on metallic surfaces the surface activity becomes very high, often of the order of 103. This means that very small amounts of these elements have a large effect on the surface energy, and that the experimental determination of reliable surface energies needs systems of extreme purity. 

H (MPa) (Eq. (13)) and HA (MPa m3 mor1) (Eq. (14)) are often referred to as Henry s constant , but they are in fact definitions which can be used for any composition of the phases. They reduce to Henry s law for an ideal gas phase (low pressure) and for infinitely dilute solution, and are Henry s constant as they are the limit when C qL (or xA) goes to zero. When both phases behave ideally, H depends on temperature only for a dilute dissolving gas, H depends also on pressure when the gas phase deviates from a perfect gas finally, for a non-ideal solution (gas or liquid), H depends on the composition. This clearly shows that H is not a classical thermodynamic constant and it should be called Henry s coefficient . 

Case 1 in Figure 45.2 refers to a case where the reaction between S and H2 is very slow. In that case, the rate of hydrogen consumed by the reaction (i.e., the rate of the reaction) is small compared to the maximum rate of mass transfer. Thus, mass transfer feeds the liquid phase easily with dissolved hydrogen. The liquid-phase hydrogen concentration is very close to that at equilibrium given by the Henry s law ... 

Sander, R. (2000), Henry s law constants. In W.G. Mallard and P.J. Lindstrom (eds.), Chemistry WebBook, NIST Standard Reference Database Number 69, National Institute of Standards and Technology, USA, http //webbook.nist.gov/chemistry. 

The tentative equation summarized in Table V allows the calculation of the solubility at one atmosphere gas partial pressure which is numerically equal to the inverse of Henry s constant (equation 1). Although Henry s law may be adequate up to moderate pressures, it requires some corrections for the solubilities at higher pressures. Table VI summarizes some approaches that have been used to correlate solubility pressure isotherms. These have been discussed in many places including references [,21 and 22]. ... 

The thermodynamic development above has been strictly limited to the case of ideal gases and mixtures of ideal gases. As pressure increases, corrections for vapor nonideality become increasingly important. They cannot be neglected at elevated pressures (particularly in the critical region). Similar corrections are necessary in the condensed phase for solutions which show marked departures from Raoult s or Henry s laws which are the common ideal reference solutions of choice. For nonideal solutions, in both gas and condensed phases, there is no longer any direct... 

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