Chemical Equilibria In Solution Research Articles

Geometrical structure of the cis- and trans-isomers of 1,2-dihaloethylenes and the energetics of their chemical equilibrium in solution

This work examines the isomeric cis—trans equilibrium of the 1,2-dihaloethylenes in several solvents (benzene, acetonitrile and water), by means of quantum chemical calculations involving the continuum model of solvation developed by Rivail's group. The need to take into account beyond the dipole moment to explain the negligible influence of the solvent on the equilibria is emphasized, in particular, if one realizes that the geometric isomer cis is a dipolar molecule whereas the trans is not. Geometrical changes induced by the solvent on both isomers are different: the CC bond distance and XCC bond angle show different trends with the solvent polarity for each isomer. These results are rationalized on the basis of the alternative role played by the dipole or quadrupole moment. The small influence of the long-range interactions on the energetics of the equilibrium can be only explained if electric multipole moments of higher order than quadrupole are considered. Cavitation and dispersion contributions have also been estimated in the case of the chloro derivative for which experimental information is available. Although these contributions are much larger than the electrostatic one, they do not discriminate between isomers, particularly when cavitation + dispersion is considered.

1H- and 13C-NMR-Spectroscopic Study of Chemical Equilibria in Solutions of Formaldehyde in Water, Deuterium Oxide, and Methanol

Reliable information on chemical equilibria in formaldehyde solutions is needed for the design of separation process for formaldehyde containing mixtures. Chemical equilibria of the poly(oxymethylene) glycol formation in formaldehyde solutions in water (and deuterium oxide) and of the poly(oxymethylene) hemiformal formation in methanolic formaldehyde solutions were studied by [sup 1]H and [sup 13]C-NMR spectroscopy. Overall formaldehyde mole fraction and temperature range from 0.06--0.19 mol/mol, 275--357 K for solutions in water and 0.17--0.50 mol/mol, 274--317 K for methanolic solutions. Chemical equilibrium constants are determined assuming ideal solution behavior. Results from [sup 1]H and [sup 13]C-NMR spectroscopy agree well. Chemical equilibria of the poly(oxymethylene) glycol formation do not depend on whether water or deuterium oxide is used. The new experimental results confirm only some of the literature data.

Chemical Equilibria in Solution, Dependence of Rate and Equilibrium Constants on Temperature and Pressure

Article Chemical Equilibria in Solution, Dependence of Rate and Equilibrium Constants on Temperature and Pressure was published on February 1, 1994 in the journal Zeitschrift für Physikalische Chemie (volume 185, issue 2).

Book Review: Chemical Equilibria in Solution. Dependence of Rate and Equilibrium Constants on Temperature and Pressure. (Physical Chemistry Series). By M. J. Blandamer

Book Review: Chemical Equilibria in Solution. Dependence of Rate and Equilibrium Constants on Temperature and Pressure. (Physical Chemistry Series). By M. J. Blandamer

Spectrophotometric determination of stability constants of anti-stepwise complexes

There is a considerable knowledge of chemical equilibria of the stepwise formation of complexes in coordination chemistry. However, the coordination equilibria of complex formation of the type, M + R ⇌ MR ⇌ M2R ⇌ M3R ⇌…⇌ MnR is less well understood. As their compositions are contrary to the formation of stepwise complexes, they are called ‘anti-stepwise complexes’. The existence of such complexes is not unusual and often causes difficulties in speciation analyses. Therefore, it is essential to investigate further the chemical equilibria in solution. In this paper, based on Bjerrum's function (n) and the method of corresponding solutions, a method is suggested for determining the stability constants of this kind of complex. For demonstration purposes it has been used with the iron(III) and Eriochrome Cyanine R system and satisfactory results were obtained. This method is generally applicable and could be used for most ‘anti-stepwise’ systems.

Modification of the high-performance liquid chromatographic retention behaviour of β-diketones by the inclusion of metal ions in the mobile phase

The effect of transition metals as components of the mobile phase in high-performance liquid chromatography on the retention of analytes containing a β-diketone chelating group has been examined. A model for the changes has been developed which takes into account the secondary chemical equilibria in solution, including the formation constants of the complexes, the pH of the model phase and the concentration of the metal ions.

Prediction of retention behaviour on modification of the mobile phase in high-performance liquid chromatography using metal ions: 2-aminophenol as a model system

A model has been developed for predicting the effect of transition metals as components of the mobile phase in high-performance liquid chromatography on the retention of an analyte containing a chelating group. It takes into account the secondary chemical equilibria in solution, including the formation constants of the complexes, the pH of the mobile phase and the concentration of the metal ions. The model was tested by comparison with data determined for the retention of 2-aminophenol on a porous polystyrene-divinylbenzene polymer column in the presence of metal ions.

Measurement of the binding capacity of casein for copper by potentiometric stripping analysis

The copper binding properties of casein were investigated; the conditional stability constant and the number of binding sites were evaluated by Potentiometric Stripping Analysis (PSA) and Gel Permeation Chromatography experiments. PSA, being insensitive to the presence of organic matter, allows measurements of the free form of the metal in normal conditions without disturbing the chemical equilibria in solution.

The separatory cylinder: A novel solvent extraction system for the study of chemical equilibrium in solution

The experiment described in this paper suggests a way of introducing students in physical chemistry to concepts such as chemical potential, the activity of a solute, the mass of action in a homogenous equilibrium, and the equilibrium distribution of a solute between two immiscible phases.

Thermodymamics and kinetics of chemical equilibrium in solution: Multipurpose experiment in the physical chemistry course

The author has devised a multipurpose physical chemistry exercise that allows the examination of both thermodymamics and kinetics of chemical equilibrium in solution.

Simplified Calculation of CACO3 Saturation at High Temperatures and Pressures in Brine Solutions

Summary A simplified method to calculate CaCO3 saturation is developed using only commonly measured field parameters. The calculated saturation index, Is, and pH values are accurate at high temperatures and pressures in brines and are compared with less sophisticated and more complex calculations. The final forms of Is and pH calculations are derived using conditional equilibrium constants dependent on temperature, pressure, and ionic strength. which eliminate the need for activity coefficients. The Is equation is presented in forms for calculation with known or derived pH and where the pH of the solution is unknown. Practical application of Is is shown by calculating the scaling tendency of several geopressured energy wells of the U.S. gulf coast region. Introduction Calcium carbonate (CaCO2) precipitation has been and continues to be a problem in aqueous systems. Calcium carbonate scale, although present at all temperature/pressure regimes, is most prevalent at high temperatures and pressures, where CaCO3 solubility is decreased with the increased temperature. Less sophisticated methods for determining scaling tendency, such as the Langelier and Stiff-Davis Is's, have built-in constraints when considering closed aqueous systems. With both methods the solution pH must be known to begin the calculations. There is no technique for reliable pH measurement at high temperatures and pressures. Neither method can account for pressure changes in the system or the changing solubility of CO2(g) with temperature or pressure. The Stiff and Davis constant K is not known above 194 degrees F. The method presented in this paper follows the Stiff and Davis method very closely at temperatures in range of the Stiff and Davis calculation and at known pH. Table 1 is a comparison of the Is presented here and the Stiff and Davis Is for four oilfield brines. 4 The method enables calculations of pH, if not known, and considers total pressure as well as varying CO2(g) partial pressures from commonly measured variables in the field-i.e., total calcium, bicarbonate alkalinity, ionic strength, temperature, pressure, and the mole fraction of CO2 in the gas phase. An effort has been made throughout the paper to maintain the resulting algorithm so it is simple enough to perform easily in the field with a handheld calculator. More complex computer codes exist for the calculation of CaCO3 scaling tendencies in aqueous systems at high temperatures and pressures, but these are constrained by the need for mainframe computers, complex codes, and large data bases. A sophisticated code, EQUILIB, developed by Shannon et al. requires computer facilities and takes pressure into account. This offers an opportunity to check the calculations presented here. Shannon et al. present two examples of results, an unflashed and a flashed brine, in their paper. The results and a comparison with Is presented in this paper are presented in Table 2, and good agreement with the more complex calculations is demonstrated. Calculation of Is The calculation of Is in brines involves changing chemical equilibria in solutions of interest with temperature, pressure, and ionic strength. The changing equilibria in the solutions can be dealt with by allowing the equilibrium constants in the governing chemical equations to vary with the changing conditions of the brines. The equilibrium constants then become conditional constants whose values depend on temperature. pressure, and ionic strength. JPT P. 1583^

Application of gas chromatographic headspace analysis to the characterization of chemical equilibria in solutions

The possibility is considered of using headspace analysis in studies of chemical equilibria in solutions of volatile organic compounds. The main theoretical relationships for the determination of the constants of X + Y ⇄ XY type equilibria by the gas chromatographic analysis of equilibrated vapour above a solution are derived. New methods are proposed and have been checked experimentally for the measurement of the ionization constants of volatile organic compounds, and of the stability constants of metal complexes with unsaturated and aromatic hydrocarbons.

82. The mechanism of additions to double bonds. Part VII. Chemical equilibrium in solution and in the gaseous state

82. The mechanism of additions to double bonds. Part VII. Chemical equilibrium in solution and in the gaseous state

LXIII.—The influence of salts on chemical equilibria in solutions

LXIII.—The influence of salts on chemical equilibria in solutions