Chemical equilibrium electrolyte solutes

Partial Molar Volume 1 0. Cryoscopic Determination of Molar Mass 1 1. Freezing-Point Depression of Strong and Weak Electrolytes 12. Chemical Equilibrium in Solution... 

Electrolyte solutions. 2. Chemical equilibrium. 3. Solution (Chemistry) I. Title. 

Outhwaite C W 1974 Equilibrium theories of electrolyte solutions Specialist Periodical Report (London Chemical Society)... 

Chapters 7 to 9 apply the thermodynamic relationships to mixtures, to phase equilibria, and to chemical equilibrium. In Chapter 7, both nonelectrolyte and electrolyte solutions are described, including the properties of ideal mixtures. The Debye-Hiickel theory is developed and applied to the electrolyte solutions. Thermal properties and osmotic pressure are also described. In Chapter 8, the principles of phase equilibria of pure substances and of mixtures are presented. The phase rule, Clapeyron equation, and phase diagrams are used extensively in the description of representative systems. Chapter 9 uses thermodynamics to describe chemical equilibrium. The equilibrium constant and its relationship to pressure, temperature, and activity is developed, as are the basic equations that apply to electrochemical cells. Examples are given that demonstrate the use of thermodynamics in predicting equilibrium conditions and cell voltages. 

If the electrolyte components can react chemically, it often occurs that, in the absence of current flow, they are in chemical equilibrium, while their formation or consumption during the electrode process results in a chemical reaction leading to renewal of equilibrium. Electroactive substances mostly enter the charge transfer reaction when they approach the electrode to a distance roughly equal to that of the outer Helmholtz plane (Section 5.3.1). It is, however, sometimes necessary that they first be adsorbed. Similarly, adsorption of the products of the electrode reaction affects the electrode reaction and often retards it. Sometimes, the electroinactive components of the solution are also adsorbed, leading to a change in the structure of the electrical double layer which makes the approach of the electroactive substances to the electrode easier or more difficult. Electroactive substances can also be formed through surface reactions of the adsorbed substances. Crystallization processes can also play a role in processes connected with the formation of the solid phase, e.g. in the cathodic deposition of metals. 

Van Luik, A.E. and Jurinak, J.J., Equilibrium chemistry of heavy metals in concentrated electrolyte solution, in Chemical Modeling in Aqueous Systems Speciation, Sorption, Solubility and Kinetics, Jenne, E.A., Ed., ACS Symp. Series 93, American Chemical Society, Washington, 1979, pp. 683-710. 

To test the validity of the extended Pitzer equation, correlations of vapor-liquid equilibrium data were carried out for three systems. Since the extended Pitzer equation reduces to the Pitzer equation for aqueous strong electrolyte systems, and is consistent with the Setschenow equation for molecular non-electrolytes in aqueous electrolyte systems, the main interest here is aqueous systems with weak electrolytes or partially dissociated electrolytes. The three systems considered are the hydrochloric acid aqueous solution at 298.15°K and concentrations up to 18 molal the NH3-CO2 aqueous solution at 293.15°K and the K2CO3-CO2 aqueous solution of the Hot Carbonate Process. In each case, the chemical equilibrium between all species has been taken into account directly as liquid phase constraints. Significant parameters in the model for each system were identified by a preliminary order of magnitude analysis and adjusted in the vapor-liquid equilibrium data correlation. Detailed discusions and values of physical constants, such as Henry s constants and chemical equilibrium constants, are given in Chen et al. (11). 

The solubility of gaseous weak electrolytes in aqueous solutions is encountered in many chemical and petrochemical processes. In comparison to vapory-liquid equilibria in non reacting systems the solubility of gaseous weak electrolytes like ammonia, carbondioxide, hydrogen sulfide and sulfur dioxide in water results not only from physical (vapor-liquid) equilibrium but also from chemical equilibrium in the liquid phase. 

King, E. J. "Acid-Base Equilibria in "The International Encyclopedia of Physical Chemistry and Chemical Physics Topic 15, Equilibrium Properties of Electrolyte Solutions" Vol. 4, Robinson, R. A., Ed., Pergamon Press, 1965 (distributed by The MacMillan Co., New York). ... 

LiPFe was proposed as an electrolyte solute for lithium-based batteries in the late 1960s, and soon its chemical and thermal instabilities were known. Even at room temperature, an equilibrium exists ... 

Equation 8.173 estabhshes that in an electrolytic solution the relative proportions of oxidized and reduced species are controlled by the redox state of the system (we will see in section 8.19 that in actual fact the redox equilibrium among the various redox couples in natural, chemically complex, aqueous solutions is rarely attained). Imposing on equation 8.173 the value of the ruling redox potential (Eh)—i.e.,... 

Nitric acid is a strong electrolyte. Therefore, the solubilities of nitrogen oxides in water given in Ref. 191 and based on Henry s law are utilized and further corrected by using the method of van Krevelen and Hofhjzer (77) for electrolyte solutions. The chemical equilibrium is calculated in terms of liquid-phase activities. The local composition model of Engels (192), based on the UNIQUAC model, is used for the calculation of vapor pressures and activity coefficients of water and nitric acid. Multicomponent diffusion coefficients in the liquid phase are corrected for the nonideality, as suggested in Ref. 57. 

The measurement of ion activities assumes chemical equilibrium between the PVC membrane and the electrolyte bearing solutions. The time domain chemical and dielectric space charge changes that occur are minimized by membrane composition and sensor design and are considered negligible during the measurement period. Hence, the potential dependence of the ion activity is characterized by the Nemst equation. The following thermodynamic expressions describe the potentials of the... 

Gas sensors usually incorporate a conventional ion-selective electrode surrounded by a thin film of an intermediate electrolyte solution and enclosed by a gas-permeable membrane. An internal reference electrode is usually included, so that the sensor represents a complete electrochemical cell. The gas (of interest) in the sample solution diffuses through the membrane and comes to equilibrium with the internal electrolyte solution. In the internal compartment, between the membrane and the ion-selective electrode, the gas undergoes a chemical reaction, consuming or forming an ion to be detected by the ion-selective electrode. (Protonation equilibria in conjunction with a pH electrode are most common.) Since the local activity of this ion is proportional to the amount of gas dissolved in the sample, the electrode response is directly related to the concentration of the gas in the sample. The response is usually linear over a range of typically four orders of magnitude the upper limit is determined by the concentration of the inner electrolyte solution. The permeable membrane is the key to the electrode s gas selectivity. Two types of polymeric material, microporous and homogeneous, are used to form the... 

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]. 

See, for example, Chap. 9 in K. Denbigh, The Principles of Chemical Equilibrium, Cambridge University Press, Cambridge, 1981. ThelUPAC recommendation for the symbol to represent rational activity coefficients is yx, which is not used in this book in order to make the distinction between solid solutions and aqueous solutions more evident. In strict chemical thermodynamics, however, all activity coefficients are based on the mole fraction scale, with the definition for aqueous species (Eq. 1.12) actually being a variant that reflects better the ionic nature of electrolyte solutions and the dominant contribution of liquid water to these mixtures. (See, for example, Chap. 2 inR. A. RobinsonandR. H. Stokes,Electrolyte Solutions, Butterworths, London, 1970.)... 

Gautam, R. and W.D. Seider, "Calculation of Phase and Chemical Equilibrium. Part III Electrolytic Solutions," Accepted for publication in AIChE Journal, 1979c. 

Under this umbrella, a number of different applications lie, amongst others the batch equilibration and equilibrium soil solution methods. According to the USEPA (1999), the former represents the most common laboratory method for determining partition coefficients—normally defined as Kd—both for contaminated sites studies and for predictions of chemicals behaviour in soils (OECD, 2002). The batch equilibration method consists of mixing a soil with a known amount of liquid (background electrolyte), which is then shaken into a slurry and allowed to equilibrate for an adequate time. The solution will be separated from the solids by centrifuging the slurry, resulting in a supernatant and a separated solid phase. The supernatant will, therefore, be removed, filtered and analysed. 

Refs. [i] Denbigh KG (1987) Principles of chemical equilibrium, 4th edn. Cambridge University Press, Cambridge [ii] Robinson RA, Stokes RH (1970) Electrolyte solutions. Butterworths, London [iii] Hamann CH, Hamnett A and Vielstich W (1998) Electrochemistry. Wiley-VCH, Wein-heim [iv] McNaught AD, Wilkinson A (1997) IUPAC Compendium of chemical terminology, 2nd edn. Blackwell Scientific Publ, Oxford [v] http //www.iupac.org/publications/compendium/index.html... 

Dissociation — is the separation or splitting of a chemical compound (complexes, molecules, or salts) into two or more -> ions by dissolution and -> solvation, or by any other means, the breaking into smaller molecules, or radicals. In case of solvation, this results in an ioni-cally conducting -> electrolyte solution. D. usually occurs in a reversible manner. The opposite process is association or recombination. Assuming a reversible dissociation reaction in a chemical -> equilibrium of the form XY X + Y, the ratio of dissociation is quantified by the dissociation constant JCn, i.e JCn = where a denotes the activity of the species. The dissociation constants are frequently quoted as values of pAT = - log K. In mass spectrometry, the term is used in the meaning of a fragmentation, i.e., a decomposition of an ion into another ion of lower mass and one or more neutral species. 

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