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J H Hildebrand

Publications and source records attributed to J H Hildebrand.

At least 19 recordsLinked to original sources
PubMed1979

An improvement in the theory of regular solutions.

In constructing the theory of regular, nonpolar, binary solutions, the partial molal energy of mixing has been expressed by the square of difference between "solubility parameters," usually evaluated by the molal energy of vaporization per cubic centimeter, (DeltaE(v)/V)(1/2) = delta, at approximately 25 degrees C. We have found, however, that liquids whose molecules contain methyl groups do not conform to these parameters; to account for their solvent power for iodine requires parameters increased in proportion to the number of methyl groups per molecule. The anomaly may be attributed to the absence of outer nonbonded electrons able to exert London attractive force between neighboring molecules. Parameters derived from solubility for iodine in both methyl-containing liquids and fluorochemicals greatly improve the predictive power of the theory of regular solutions.

Journal Article↗
PubMed1979

Forum on osmosis. II. A criticism of "solvent tension" in osmosis.

Concepts about the liquid state that are inconsistent with the facts are noted, and solvent under tension is one of them. Osmosis is not present in a solution: it is a process in the presence of a semipermeable membrane that can be quantified by the operation of applying a hydrostatic pressure. The classical derivation of the van't Hoff equation from Raoult's law is reviewed. The soundness of the early views of G. H. Lewis has not changed.

Chemical Phenomena↗
PubMed1976

Viscosity of dilute gases and vapors.

The well-known formula for calculating the viscosity of hard sphere gases, eta(o) = 2(mkT)(1/2)/3pi(3/2)sigma(2), where sigma(2) is molecular cross section, is altered to eta(o) = K(MT)(1/2)/V(t) (2/3), where V(t) is the molal volume of a liquid that has expanded sufficiently to permit mean free paths long enough to have significant fractions of the random thermal momenta of molecules in free flight and M is molal mass.This formulation places upon a single straight line points for all nonpolar molecules, mono- and polyatomic molecules alike, over long ranges of temperature.

Journal Article↗
PubMed1976

Viscosity of liquid metals: An interpretation.

The fluidity of liquid metals, like that of simple nonmetallic liquids, is a linear function of the ratio of unoccupied volume to intrinsic volume over long ranges as expressed by the equation varphi = B[(V/V(0)) - 1]. Values of V(0) obtained by extrapolating to varphi = 0 agree well with molal volumes of compact crystals at 20 degrees C calculated from densities.Values of the ratio varphi/[(V/V(0)) - 1] range from 27.0 for Na to 1.55 reciprocal centipoise for Ni. Viscosities at ratios of expansion V/V(0) = 1.10 vary linearly with squares of solubility parameters DeltaE(v)/V(0), where DeltaE(v) is molal energy of vaporization at the melting point. Viscosities at 10% expansion range from 0.037 cP for Na to 5.38 cP for Co, with some divergence for metals with values of eta in the neighborhood of unity. The good agreement in the case of the transition metals Cu, Fe, Co, and Ni we attribute to distribution of vector momentum among quasi-chemical bonds between d-electrons and vacant orbitals.

Journal Article↗
PubMed1975

Kinetic theory of viscosity of compressed fluids.

THE VISCOSITY OF A COMPRESSED GAS IS A FUNCTION OF THREE VARIABLES: (1) the degree of crowding of the molecules; (2) their capacity, by reason of softness, flexibility, or rotational inertia, to absorb the vector momentum applied to cause flow; (3) the resistance to this vector momentum offered by the randomly oriented thermal momenta, which becomes significant when the liquid expands sufficiently to permit molecular mean free paths between binary collisions to be long enough for thermal momenta to acquire fractions of their thermal momentum in free space.The fluidity varphi of simple liquids obeys the linear equation varphi = B(V - V(0))/V(0) and its viscosity is, therefore, eta(a) = V(0)/B(V - V(0)); this accounts for components 1 and 2. The contribution of random thermal momenta, 3, obeys the equation, eta(b) = eta(0)(1 - V(t)/V). eta(0) is the viscosity of the dilute gas; V(t) is the molal volume at which the thermal contribution begins. The total momentum, eta = eta(a) + eta(b).Values of eta(0) vary linearly with T(1/2). Values of V(t) are related to heat capacities.

Journal Article↗
PubMed1974

Diffusivity of Methane in a Mixture of CCl(4) and c-C(6)F(11)C(2)F(5) of the Critical Composition in the Region above the Temperature of Separation.

The diffusivity of CH(4) in a mixture of CCl(4) and c-C(6)F(11)C(2)F(5) of the critical composition in the region of temperature close to that of unmixing, decreases as in a homogeneous liquid from 36 degrees to about 32 degrees . It then passes through a minimum of 10(5)D approximately 4.15 cm(2)/sec at about 27.5 degrees , then rises to 10(5)D = 4.61 at 25.00 degrees , then steeply to 6.36 cm(2)/sec in the further drop of only 0.3 degrees to 24.71 degrees .

Journal Article↗
PubMed1974

Diffusivity of gases in liquids.

Diffusion coefficients of H(2), Ne, N(2), Ar, CH(4), Cl(2), CF(4), C(2)H(6), SF(6), I(2), and isotopic CCl(4), all in CCl(4), determined at atmospheric pressure, are linear functions of temperature, converging to zero at the temperature where CCl(4) ceases to be fluid. The slopes of these lines increase with decreasing molecular cross-section of the diffusants, and with increasing entropy of expansion of the diffusants in CCl(4). Diffusivities in (C(4)F(9))(2)N, whose molecules are very large and three-armed, do not converge as temperature is decreased. Molecules of H(2), Ne, and, to a lesser extent, Ar, are able to diffuse in (C(4)F(9))(2)N even at temperatures where fluidity is low.

Journal Article↗
PubMed1972

Fluidity: a general theory.

The equation varphi = B(V - V(o))/V(o), which reproduces the fluidity of simple liquids accurately over ranges between freezing and boiling points, is here shown to hold to pressures of at least 500 atm, and nearly to critical volumes. Fluidity can vary continuously above the critical region into that of compressed gas, where the parameter B becomes a function of temperature.The parameter V(o) is a "corresponding states" fraction of the critical molal volume. It is identical with the molal volume of the solid only in cases where molecules are free to rotate as they do in the liquid.Parameter B is a measure of the extent to which the external momentum that produces viscous flow is absorbed by the molecules of the liquid. Such damping can result from molecular mass, e.g., Ne, Ar, Kr; flexibility, normal alkanes; or rotational inertia, SiBr(4) against SiCl(4).

Journal Article↗
PubMed1969

Relative diffusivities of methane in water and carbon tetrachloride.

Methane diffuses in water at 25 degrees C 3/5 as fast as it does in carbon tetrachloride. Since diffusivity depends mainly upon temperature, viscosity of the solvent, and molecular cross section of the diffusant, and since viscosities of H(2)O and CCl(4) at 25 degrees C are almost identical, one may infer that molecules of CH(4) in H(2)O are not imprisoned in "icebergs," and are retarded only by hydrogen bonds, not by encounters with "ice-like" aggregates.

Journal Article↗
PubMed1969

Thermodynamic parameters for dissolved gases.

In 1958 and subsequently we correlated properties of solutions of gases in liquids by using the "force constants," epsilon/k, and collision diameters, sigma, which serve as parameters in equations for molecular pair potential energy such as that of Lennard-Jones or its variants. Unfortunately, however, the figures for these parameters that have been published are so scattered for the same gas as to make it difficult to select "best" values; in 1967, therefore, I substituted for these indirectly determined molecular parameters the directly and accurately known molal energy of vaporization, DeltaE(b) (v), and the molal volume, v(b), of the liquefied gas, both at its boiling point. A plot of values of DeltaE(2) (v) against the most trustworthy values of epsilon/k reveals direct proportionality. The same is true for V(b) (1/3) versus sigma.Recent examples will be shown of excellent linear correlations with these parameters of thermodynamic properties of different gases in the same solvent.It is no less "scientific" and far more practical to regard molecules of a solute as immersed in the potential energy field of its solvent than it is to split this field into imperfectly known pair potentials of questionable additivity and to try to integrate them over an undetermined distribution function.

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