Ionic reactions equilibrium constant

From Eqn. (14) it follows that with an exothermic reaction - and this is the case for most reactions in reactive absorption processes - decreases with increasing temperature. The electrolyte solution chemistry involves a variety of chemical reactions in the liquid phase, for example, complete dissociation of strong electrolytes, partial dissociation of weak electrolytes, reactions among ionic species, and complex ion formation. These reactions occur very rapidly, and hence, chemical equilibrium conditions are often assumed. Therefore, for electrolyte systems, chemical equilibrium calculations are of special importance. Concentration or activity-based reaction equilibrium constants as functions of temperature can be found in the literature [50]. 

In solutions of ionic strength of approximately 0.25 M, a hydrogen ion dissociates from HATP3- with an acid-base pK of approximately 6.47 [5], where pK is defined as — log10 Keq and Keq is the dissociation reaction equilibrium constant. The equilibrium expression is ... 

Reaction rate and equilibrium change greatly around the critical point due to the variation in properties of water. Various models have been proposed for describing the variation of reaction rate or equilibrium over a range of supercritical state (9-12). The effect of the dielectric constant on ionic reactions can be expressed by the Born equation, which expresses electrostatic interactions of ions in a dielectric field (13). It is widely known that the Helgeson-Kirkham-Homers (HKF) model that uses this term can describe successfully the change of ionic reaction equilibrium, although five reference state parameters should be known. 

Table 2.6. Equilibrium constants from complexation of 2.4a, 2.4b, and 2.4d to different metal ions (Kj) and second-order rate constants for the Diels-Alder reaction of these complexes with 2 (%cd) in water at 2.00 M ionic strength and 25°C. ...

Several features of equation 6.50 deserve mention. First, as the ionic strength approaches zero, the activity coefficient approaches a value of one. Thus, in a solution where the ionic strength is zero, an ion s activity and concentration are identical. We can take advantage of this fact to determine a reaction s thermodynamic equilibrium constant. The equilibrium constant based on concentrations is measured for several increasingly smaller ionic strengths and the results extrapolated... 

Given the following descriptions of reversible reactions, write a balanced net ionic equation (simplest whole-number coefficients) and die equilibrium constant expression (X) for each. 

It can be shown from a consideration of the overall stability constants of the ions [Ni( CN)4] 2 " (1027) and [ Ag( CN)2 ] (1021) that the equilibrium constant for the above ionic reaction is 1015, i.e. the reaction proceeds practically completely to the right. An interesting exercise is the analysis of a solid silver halide, e.g. silver chloride. 

The reaction is generally believed to proceed via the formation of ionic acylam-monium intermediate compounds (Reaction 1, Scheme 2.27). The equilibrium constant of the acylammonium formation depends mostly on steric and resonance factors, while the basicity of the tertiary amine seems to play a secondary role.297 In die case of the less basic compounds, such as acidic phenols, and of strong tertiary amines, such as Uialkylamines, the reaction has been reported to proceed through a general base mechanism via the formation of hydroxy-amine H-bonded complexes (Reaction 2, Scheme 2.27).297... 

A final point to bear in mind is that, when a reaction involves fully dissociated ionic compounds in solution, then the equilibrium constant should be written for the net ionic equation, by using the activity for each type of ion. 

Self-Test 9.2A Write the equilibrium constant for the reaction of silver nitrate with I sodium hydroxide 2 AgN03(aq) + 2 NaOH(aq) Ag20(s) + 2 NaN03(aq) + i H20(1). Remember to use the net ionic equation. 

Nevertheless, chemical methods have not been used for determining ionization equilibrium constants. The analytical reaction would have to be almost instantaneous and the formation of the ions relatively slow. Also the analytical reagent must not react directly with the unionized molecule. In contrast to their disuse in studies of ionic equilibrium, fast chemical reactions of the ion have been used extensively in measuring the rate of ionization, especially in circumstances where unavoidable irreversible reactions make it impossible to study the equilibrium. The only requirement for the use of chemical methods in ionization kinetics is that the overall rate be independent of the concentration of the added reagent, i.e., that simple ionization be the slow and rate-determining step. 

The thermodynamic stability of a complex ML formed from an acceptor metal ion M and ligand groups L may be approached in two different but related ways. (The difference between the two approaches lies in the way in which the formation reaction is presented.) Consistent with preceding sections, an equilibrium constant may be written for the formation reaction. This is the formation constant Kv In a simple approach, the effects of the solvent and ionic charges may be ignored. A stepwise representation of the reaction enables a series of stepwise formation constants to be written (Table 3.5). 

By arguments very similar to those used to derive Eqs. (87)-(89), one can show that the equilibrium constants for exchange reactions of ionic vapor dimer molecules... 

Sigma (a) bonds Sigma bonds have the orbital overlap on a line drawn between the two nuclei, simple cubic unit cell The simple cubic unit cell has particles located at the corners of a simple cube, single displacement (replacement) reactions Single displacement reactions are reactions in which atoms of an element replace the atoms of another element in a compound, solid A solid is a state of matter that has both a definite shape and a definite volume, solubility product constant (/ p) The solubility product constant is the equilibrium constant associated with sparingly soluble salts and is the product of the ionic concentrations, each one raised to the power of the coefficient in the balanced chemical equation, solute The solute is the component of the solution that is there in smallest amount, solution A solution is defined as a homogeneous mixture composed of solvent and one or more solutes. 

The procedure of Beutier and Renon as well as the later on described method of Edwards, Maurer, Newman and Prausnitz ( 3) is an extension of an earlier work by Edwards, Newman and Prausnitz ( ). Beutier and Renon restrict their procedure to ternary systems NH3-CO2-H2O, NH3-H2S-H2O and NH3-S02 H20 but it may be expected that it is also useful for the complete multisolute system built up with these substances. The concentration range should be limited to mole fractions of water xw 0.7 a temperature range from 0 to 100 °C is recommended. Equilibrium constants for chemical reactions 1 to 9 are taken from literature (cf. Appendix II). Henry s constants are assumed to be independent of pressure numerical values were determined from solubility data of pure gaseous electrolytes in water (cf. Appendix II). The vapor phase is considered to behave like an ideal gas. The fugacity of pure water is replaced by the vapor pressure. For any molecular or ionic species i, except for water, the activity is expressed on the scale of molality m ... 

With an aqueous fluid phase of high ionic strength, the problem of obtaining activity coefficients may be circumvented simply by using apparent equilibrium constants expressed in terms of concentrations. This procedure is recommended for hydro-metallurgical systems in which complexation reactions are important, e.g., in ammonia, chloride, or sulfate solutions. 

Equilibrium Constant (K) An expression that relates the equilibrium concentrations (or pressures) of reactive species to one another. Its value is dependent on temperature, pressure, and the ionic strength of the solution in which the reaction is occurring. 

LIQUID-PHASE BEHAVIOR. The liquid phase contains dissolved substances and contacts the solid phase. For our purposes, the liquid phase is used synonymously with aqueous phase , and all processes discussed in this section take place in aqueous solutions. The dissolved monomers of the solid phase are formed in equilibrium with their uncomplexed components. Such components may be uncomplexed ions (which are charged atoms or molecules) free in solution or ionic complexes in equilibrium with dissociated ions. Concentrations of the uncomplexed ions, therefore, depend upon the concentrations of all chemical substances competing for binding interactions with them. Each complex-ation reaction is defined by either a solution equilibrium constant ... 

The equilibrium constant of an enzyme-catalyzed reaction can depend greatly on reaction conditions. Because most substrates, products, and effectors are ionic species, the concentration and activity of each species is usually pH-dependent. This is particularly true for nucleotide-dependent enzymes which utilize substrates having pi a values near the pH value of the reaction. For example, both ATP" and HATP may be the nucleotide substrate for a phosphotransferase, albeit with different values. Thus, the equilibrium constant with ATP may be significantly different than that of HATP . In addition, most phosphotransferases do not utilize free nucleotides as the substrate but use the metal ion complexes. Both ATP" and HATP have different stability constants for Mg +. If the buffer (or any other constituent of the reaction mixture) also binds the metal ion, the buffer (or that other constituent) can also alter the observed equilibrium constant . ... 

The use of Haldane relationships to verify the magnitude of the equilibrium constant or, conversely, to determine (or verify) one of the kinetic parameters requires that aU constants be measured under the same experimental conditions (eg., temperature, pH, buffer species, ionic strength, free metal ion concentrations, etc) If not, the Haldane relationship has no meaning. In addition, kinetic data are often limited in precision, unlike equilibrium measurements. For multisubstrate reactions, there are at least two different Haldane relationships. Thus,... 

It should also be mentioned here that many of the chemical reactions which have been "explained with the HSAB model (2) occur in polar solvents and many involve the formation of ionic species. Thermodynamic cycles can be constructed for these reactions which show how many different kinds of effects are operative. When one considers that much of the data involve rate constant and equilibrium constant measurements, the explanation of this data becomes even more complex for there are entropy terms as well as enthalpy terms for all the steps in any cycle that is constructed. Even less information is available concerning these steps than we had above for the coordination model yet explanations are offered based solely on one step (4) — the strength of the bonding. 

All data sets are from V. Pakti (Ed.), Tables of Rate and Equilibrium Constants of Heterolytic Organic Reactions, Vol. 1(1), VINTTI, Moscow, 1975, unless otherwise noted. Superscript numbers indicate temperature other than 25° C. I is ionic strength. 

Baes and Mesmer [161] have suggested that McDowell and Johnston s data can be satisfactorily explained in terms of only the tetrahydroxy species if one allows for the probable effect of increasing ionic strength. However, this statement is presumably incorrect as McDowell and Johnston reported their equilibrium constant in terms of activities, and kinetic measurements on the complexation reactions of Cu(II) at pH > 13 indicate that two different hydroxy species exist [165]. 

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