Aquatic chemistry reactions

In aquatic chemistry, the unitary proton level of the proton dissociation reaction is expressed by the logarithm of the reciprocal of the proton dissociation constant i.e. p = - log K here, a higher level of proton dissociation corresponds with a lower pK. When the pKy of the adsorbed protons is lower than the pH of the solution, the protons in the adsorbed hydronium ions desorb, leave acidic vacant proton levels in adsorbed water molecules, and form hydrated protons in the aqueous solution. Fig. 9-22 shows the occupied and vacant proton levels for the acidic and basic dissociations of adsorbed hydronium ions and of adsorbed water molecules on the interface of semiconductor electrodes. 

Faust, B. C., Aquatic photochemical reactions in atmospheric surface, and marine waters Influences on oxidant formation and pollutant degradation . In The Handbook of Environmental Chemistry, Vol. 2, Part L, P. Boule, Ed., Springer, Berlin, 1999, pp. 101-122. 

Concentrations of bicarbonate and calcium in many rivers conform to the mass balance for Reaction A [HC03 ] 2[Ca24 ]. [Data from w. stumm and J. J. Morgan, Aquatic Chemistry, 3rd ed. (New York Wiley-lnterscience. 1996). p. 189 and H. D. Holland. The Chemistry of the Atmosphere and Oceans (New York Wiley-lnterscience, 1978).]... 

This approach will be rigorous if a complete speciation calculation is done for P and E (as described in standard textbooks of aquatic chemistry) and all the necessary values of ki are available. Fortunately, the analysis can usually be simplified to reaction between one or two dominant species, and most of the available rate constants are for these same species. 

Equilibrium models provide information about the chemistry of the system at equilibrium but will not tell you anything about the kinetics with which the system reached equilibrium state. The basic objectives in using equilibrium models in estuarine/aquatic chemistry is to calculate equilibrium compositions in natural waters, to determine the amount of energy needed to make certain reactions occur, and to ascertain how far a system may be from equilibrium. 

The catalytic role of microorganisms in redox reactions is discussed in exemplary fashion in Chap. 7 of F. M. M. Morel, Principles of Aquatic Chemistry, Wiley, New York, 1983. 

Components are species whose concentrations can be varied independently (in a mathematical sense) and whose combination in reactions can produce all other species in an aqueous system. The number of components is unique to a given system, but not their identity, which is chosen for convenience in developing a thermodynamic (or kinetics) description. For an excellent discussion of equilibrium speciation calculations in terms of components, see Chap, 3 in F. M. M. Morel, Principles of Aquatic Chemistry, Wiley, New York, 1983. 

Wehrli, B., Friedl, G., and Manceau, A., Reaction rates and products of manganese oxidation at the sediment-water interface, in Advances in Chemistry Series 244, Aquatic Chemistry Interfacial and Interspecies Processes, Huang, C.P., O Melia, C.R., and Morgan, J.J., Eds., American Chemical Society, Washington, D.C., 1992, p. 111. 

This reaction and the corresponding one for anions turn out to be useful prototypes for a number of Lewis acid properties of fundamental importance in aquatic chemistry, bioinorganic chemistry, and inorganic chemistry itself Six broadly applicable categories of the acid-base reactivity of cations and anions have been defined (Table 1) ... 

Aquatic chemistry is concerned with the chemical reactions and processes affecting the distribution and circulation of chemical species in natural waters. The objectives include the development of a theoretical basis for the chemical behavior of ocean waters, estuaries, rivers, lakes, groundwaters, and soil water systems, as well as the description of processes involved in water technology. Aquatic chemistry draws primarily on the fundamentals of chemistry, but it is also influenced by other sciences, especially geology and biology. 

Our understanding of natural water systems has, until recently, been seriously limited by a lack of kinetic information on critical reactions in water, in sediments, and at interfaces. Earlier in atmospheric chemistiy (Seinfeld, 1986) and more recently in aquatic chemistry (Brezonik, 1993), a considerable growth of information on rates and mechanisms for reactions central to environmental chemistry has taken place. As a result, we are now better able to assess the characteristic time scales of chemical reactions in the environment and compare these with, for example, residence times of water in a system of interest. Schematically, as shown here, for chemical vs. fluid time scales... 

FIGURE 1-9 Temperature dependence of several common chemical reactions occurring in water. Although temperature may often be neglected in approximate calculations, for maximum accuracy, equilibrium constants must be corrected for the temperature of the chemical system of interest [adapted from Principles and Applications of Aquatic Chemistry, by F.M.M. Morel andJ.G. Hering. Copyright 1993, John Wiley Sons, Inc. Reprinted by permission of John Wiley Sons, Inc.]. 

Stumm, W. Morgan, J.J. (1996) Aquatic Chemistry. 3rd Edn. Wiley-Interscience, New York, NY. Sullivan, L.A., Bush, R.T. McConchie, D.M. (2000) A modified chromium-reducible sulfur method for reducing inorganic sulfur optimum reaction time for acid sulfate soil. Aust. J. Soil Res., 38,... 

Fortunately, equation (1) is adequate for most solution reactions near room temperature, and several computer equilibrium models make these corrections if the required enthalpy values are available. Unfortunately, enthalpy data for many important solution species (e.g., metal ion species and ion pairs) have not been determined. In a few instances the temperature dependence of a reaction is very well known. A particularily relevant example for aquatic chemistry is log K for water which is given by. 

Further progress in this expanding field of aquatic chemistry will be made along with recent advances in (a) the thermodynamics md kinetics of specia-tion reactions in sea water (Mantoura et al., 1978 Whitfield and Turner, 1978) and (b) in correlating the electrochemical with the biological availability and transport mechanisms of the various organic complexes and their synthetic analogues (O Shea and Mancy, 1976 Raspor et al., 1977 Turner and Whitfield, 1979). 

Jaffe D. A. (1992) The nitrogen cycle. In Global biogeochemical cycles (Ed. S. S. Butcher, R. J. Charlson, G. H. Orian and G. V. Wolfe), Acad. Press, London, pp. 263-284 Jang, M., Czoschke, N. M., S. Lee and K. M. Kamens (2002) Heterogeneous atmospheric aerosol production by acid-catalyzed particle-phase reactions. Science 298, 814-817 Jensen, J. N. (2003) A problem-solving approach to aquatic chemistry. John Wiley Sons Inc., 480 pp. 

Many of the phenomena in aquatic chemistry and geochemistry involve sedation equilibrium. In a general sense, solution equilibrium deals with the extent to which reversible acid-base, solubilization (predpitation), complexation, or oxidation-reduction reactions proceed in a forward or backward direction. This is expressed for a generalized equilibrium reaction... 

This chapter emphasizes several aspects of chemistry. It begins with a brief discussion of the nature of matter and the states of matter. Next follows a discussion of the fundamental subatomic particles that make up all matter and explains how these are assembled to produce atoms. In tnm, atoms join together to make compounds. Chemical reactions and chemical equations that represent them are discussed. Solution chemistry is especially important to aquatic chemistry and is addressed in a separate section. The important, vast discipline of organic chemistry is crucial to all parts of the environment and is addressed in Chapter 20. 

Most of the examples in this chapter use extent of reaction (e) as a computation tool. For aquatic chemistry, the charge-balance computation tool is often more satisfactory. 

Surfactants have also been of interest for their ability to support reactions in normally inhospitable environments. Reactions such as hydrolysis, aminolysis, solvolysis, and, in inorganic chemistry, of aquation of complex ions, may be retarded, accelerated, or differently sensitive to catalysts relative to the behavior in ordinary solutions (see Refs. 205 and 206 for reviews). The acid-base chemistry in micellar solutions has been investigated by Drummond and co-workers [207]. A useful model has been the pseudophase model [206-209] in which reactants are either in solution or solubilized in micelles and partition between the two as though two distinct phases were involved. In inverse micelles in nonpolar media, water is concentrated in the micellar core and reactions in the micelle may be greatly accelerated [206, 210]. The confining environment of a solubilized reactant may lead to stereochemical consequences as in photodimerization reactions in micelles [211] or vesicles [212] or in the generation of radical pairs [213]. 

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