Chemical equilibrium association

It is known that the order of acidity of hydrogen halides (HX, where X = F, Cl, Br, I) in the gas phase can be successfully predicted by quantum chemical considerations, namely, F < Cl < Br < I. However, in aqueous solution, whereas hydrogen chloride, bromide, and iodide completely dissociate in aqueous solutions, hydrogen fluoride shows a small dissociation constant. This phenomenon is explained by studying free energy changes associated with the chemical equilibrium HX + H2O + HjO in the solu-... 

Chemical equilibrium for a reaction is associated with the change in Gibbs free energy (AG ) ealculated as follows ... 

In terms of levels, nnderstanding the notion of chemical equilibrium involves being able to mentally translate between the macro level, conceived in terms of the observable properties (e g. colour) the sub-micro level, conceived as being identities of the specific species involved and their associated behaviour the symbolic... 

The choice of specific systems where readily perceived changes of properties were associated with changes in the controlling chemical equilibrium enabled explanation in general and prediction in particular to be finked to behavioural changes. 

Ferreira, P. F. M., Justi, R. (2005). From chemical reaction to chemical equilibrium Learning through modelling. Paper presented at the V Conference of the European Seienee Education Research Association, Barcelona, Spain, 28 August-01 September. 

This model is similar to the associated species model in that a chemical equilibrium is assumed between existing species, and it is different in that in the latter only a nonassociated ionic species is assumed to be the electrically conducting species. 

The dynamic dissociation model resembles the association (or dissociation) model in that electrically conducting species are assumed to he nonassociated species, and it differs from the association model in that in the dynamic dissociation model the dissociation process itself is the electrically conducting process, while in the association model, the amount of the dissociated species is constant according to the chemical equilibrium. 

Chemical equilibrium. The polymer concentrations in the ideal gas phase of water are related to the association equilibrium constants according to the expression ... 

STANJAN The Element Potential Method for Chemical Equilibrium Analysis Implementation in the Interactive Program STANJAN, W.C. Reynolds, Thermosciences Division, Department of Mechanical Engineering, Stanford University, Stanford, CA, 1986. A computer program for IBM PC and compatibles for making chemical equilibrium calculations in an interactive environment. The equilibrium calculations use a version of the method of element potentials in which exact equations for the gas-phase mole fractions are derived in terms of Lagrange multipliers associated with the atomic constraints. The Lagrange multipliers (the element potentials ) and the total number of moles are adjusted to meet the constraints and to render the sum of mole fractions unity. If condensed phases are present, their populations also are adjusted to achieve phase equilibrium. However, the condensed-phase species need not be present in the gas-phase, and this enables the method to deal with problems in which the gas-phase mole fraction of a condensed-phase species is extremely low, as with the formation of carbon particulates. 

Under fuel cell operation, a finite proton current density, 0, and the associated electro-osmotic drag effect will further affect the distribution and fluxes of water in the PEM. After relaxation to steady-state operation, mechanical equilibrium prevails locally to fix the water distribution, while chemical equilibrium is rescinded by the finite flux of water across the membrane surfaces. External conditions defined by temperature, vapor pressures, total gas pressures, and proton current density are sufficient to determine the stationary distribution and the flux of water. 

The interaction between the ions is regarded as a chemical equilibrium. The resulting product of such an association between two individual kinds of ions is called a complex species, and the extent to which these various complex species occurs are described in terms of the equilibrium constants. 

Speciation is a dynamic process that depends not only on the ligand-metal concentration but on the properties of the aqueous solution in chemical equilibrium with the surrounding solid phase. As a consequence, the estimation of aqueous speciation of contaminant metals should take into account the ion association, pH, redox status, formation-dissolution of the solid phase, adsorption, and ion-exchange reactions. From the environmental point of view, a complexed metal in the subsurface behaves differently than the original compound, in terms of its solubility, retention, persistence, and transport. In general, a complexed metal is more soluble in a water solution, less retained on the solid phase, and more easily transported through the porous medium. 

REDOX HALF-REACTIONS. Electron transfer reactions involve oxidation (or loss of electrons) of one component and reduction (or gain of electrons) by a second component. Therefore, a complete redox reaction can be treated as the sum of two half-reactions such that the stoichiometry and electric charge is balanced across a chemical equilibrium. For each such half-reaction, there is an associated standard potential E°. The hydrogen ion-hydrogen gas couple is ... 

Medium-chain alcohols such as 2-butoxyethanol (BE) exist as microaggregates in water which in many respects resemble micellar systems. Mixed micelles can be formed between such alcohols and surfactants. The thermodynamics of the system BE-sodlum decanoate (Na-Dec)-water was studied through direct measurements of volumes (flow denslmetry), enthalpies and heat capacities (flow microcalorimetry). Data are reported as transfer functions. The observed trends are analyzed with a recently published chemical equilibrium model (J. Solution Chem. 13,1,1984). By adjusting the distribution constant and the thermodynamic property of the solute In the mixed micelle. It Is possible to fit nearly quantitatively the transfer of BE from water to aqueous NaDec. The model Is not as successful for the transfert of NaDec from water to aqueous BE at low BE concentrations Indicating self-association of NaDec Induced by BE. The model can be used to evaluate the thermodynamic properties of both components of the mixed micelle. 

Those chlorites associated with mixed layered clay minerals are most silica-rich and have the greatest compositional variations for grains in a single thin section they tend to be iron-rich and aluminous. One chlorite vein was found to transect a glauconite pellet. This chlorite was quite iron-poor indicating attainment of a local chemical equilibrium between chlorite and iron mica upon its crystallization. 

The underlying idea is the restorative tendency of equilibrium, tending to counteract the effects of attempted changes on an original equilibrium system. This restorative tendency is associated with the stability of chemical equilibrium, and we therefore use the rigorous stability condition (8.13) to prove the above statement of Le Chatelier s principle in a general form. 

Third, write what you know and do not know. You are asked for the pH of a basic solution, so you will first have to find the [OH-]. Let [OH-] = x. Because NH and OH- ions are formed in equal amounts, [NHJ] also equals x. Of the original 0. lOOmole/liter ofNH3,x moles/liter will dissociate and leave (0.100 — x) mole/liter at equilibrium. Associate these concentrations with the chemical equation, and substitute them into the K, expression. 

This table is a supplement to Table I. It gives equations for the electron-transfer steps, and for (he chemical reactions associated with them, that are involved in the half-reactions undergone by the compounds listed in Table I, and it also gives values of the rate and equilibrium constants of these processes. 

Reversible processes are those processes that take place under conditions of equilibrium that is, the forces operating within the system are balanced. Therefore, the thermodynamics associated with reversible processes are closely related to equilibrium conditions. In this chapter we investigate those conditions that must be satisfied when a system is in equilibrium. In particular, we are interested in the relations that must exist between the various thermodynamic functions for both phase and chemical equilibrium. We are also interested in the conditions that must be satisfied when a system is stable. 

A rational deduction of elemental abundance from solar and stellar spectra had to be based on quantum theory, and the necessary foundation was laid with the Indian physicist Meghnad Saha s theory of 1920. Saha, who as part of his postdoctoral work had stayed with Nernst in Berlin, combined Bohr s quantum theory of atoms with statistical thermodynamics and chemical equilibrium theory. Making an analogy between the thermal dissociation of molecules and the ionization of atoms, he carried the van t Hoff-Nernst theory of reaction-isochores over from the laboratory to the stars. Although his work clearly belonged to astrophysics, and not chemistry, it relied heavily on theoretical methods introduced by and associated with physical chemistry. This influence from physical chemistry, and probably from his stay with Nernst, is clear from his 1920 paper where he described ionization as a sort of chemical reaction, in which we have to substitute ionization for chemical decomposition. [81] The influence was even more evident in a second paper of 1922 where he extended his analysis. [82]... 

We assume that no surfactant is present in the oil phase, and the main problem to be solved is to determine the relation between the concentrations of alcohol in the water and oil phases. A theory for the partition of the alcohol between oil and water, at chemical equilibrium, which takes into account the self-association of alcohol in the oil phase, is detailed in Appendix C. The equation that relates the mole fraction of the alcohol in the oil phase to the mole fraction of the alcohol in the water phase has the form... 

This large shift is certainly connected with the association or polymerization process. At 172° practically all the molecules exist as single molecules and at 25° they all exist as dimers. At intermediate temperatures where density measurements have proved that both forms exist in chemical equilibrium, there should be evidence of the existence of both bands. The doublet character of of the graphs for 64° and 82° shows that both these bands are present and confirms the basic assumptions. 

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