Decrease In Molar Volume Research Articles

Ultrasonic measurements and other allied parameters of praseodymium and neodymium palmitates in mixed organic solvents

Ultrasonic measurements on praseodymium and neodymium palmitates were made in a mixture of 60% benzene and 40% dimethyl sulfoxide (V/V), to determine the critical micelle concentration (CMC), soap-solvent interaction, and various acoustic and thermodynamic parameters. The values of the CMC increase with the increase in the size of the cation in the soap molecules. The ultrasonic velocity, specific acoustic impedance, apparent molar compressibility, apparent molar volume and relative association increase while the adiabatic compressibility, intermolecular free length, solvation number, molar sound velocity and available volume decrease with increasing soap concentration.

High Energy Neutron Spectroscopy of Compressed Solid Para-Hydrogen

The deep inelastic neutron scattering study of solid hydrogen at 12 K at a molar volume of 23.0 cm3 by Langel et al. has been extended to 19.5 K para-hydrogen samples compressed to molar volumes of 21.2, 19.5, and 18.3 cm3, respectively. In each case, inelastic scattering peaks were observed at energy transfers a) shifted due to the molecular translational recoil energy plus internal rotational excitation and b) broadened due to the translational motion of the initial single-particle ground state. The data are analyzed directly to yield the average kinetic energy <KE> of the ground state center-of-mass translational motion as a function of molar volume in this quantum solid. Over a 20% decrease in molar volume, <KE> values increase from 76±9 to 141±9 K. These are compared to indirect measurements.

Physical characterization and pressure—temperature microscopy of the pyrite—pyrrhotite transformation

Structural changes occurring during the hydrogen-assisted pyrite-pyrrhotite transition are characterized over the temperature range 400–600 °C. Newly developed pressure-temperature microscopy gave in-situ observations of pyrite decomposition at elevated temperatures and gas pressures. Composition of pyrrhotites was measured by X-ray diffraction and correlated with krypton surface areas. Surface areas increased with an increase in pyrite reduction due to a decrease in molar volume accompanied by the development of porosity. Increases in specific surface area are inversely proportional to the reduction temperature. Heats of adsorption of krypton on pyrite increase linearly with increases in the relative amount of the (100) crystallographic faces.

Kinetics of the solvolysis of trans-dichlorobis(1,2-diaminoethane)cobalt(III) ion in water and in water + propan-2-ol

Rates of the first-order solvolysis of trans-dichlorobis(1,2-diaminoethane)cobalt(III) ions have been measured for a range of temperatures in water and in mixtures of water with propan-2-ol, a co-solvent known for its ability to induce the formation of solvent structure at low concentrations. A plot of log (rate constant) against the Y-factor is linear, but a non-linear plot is found for log (rate constant) against reciprocal of dielectric constant. Minima in the transition-state parameters observed at mole fractions of propan-2-ol where the decrease in the partial molar volume of propan-2-ol has a minimum suggest that solvent structure has a considerable influence on the rate. The application of a free-energy cycle to the process (initial state)→(transition state) in water and in the mixture shows that changes in solvation of the transition state have a dominant effect on the rate in this region of solvent composition.

Solution Hydrates of Aqueous Non-electrolytes

FRANKS and Johnson1 recently developed a computer method for the accurate determination of partial molar quantities from the measured total properties of binary systems. In their treatment of the volume of aqueous ethyl alcohol solutions, an unexpectedly complex and apparently anomalous variation of the ethyl alcohol partial molar volume was revealed at 0.06 alcohol mole fraction over the temperature-range 0°–30° C. In addition to the known2 increase of the water solvent partial molar volume and the decrease of the alcohol partial molar volume to a minimum at about 0.08 alcohol mole fraction, the alcohol partial molar volume-concentration contour furnished1 a hitherto unobserved change in course at 0.06 alcohol mole fraction appearing as a shoulder at 10° C. which progressively developed with increasing temperature to furnish a small but definite peak at 30° C.