Chemical equilibrium computer

Estimates of Composition. The best approach toward estimating the chemistry of most contaminant species is to assume chemical equilibrium. Computer programs and databases (qv) for calculating chemical equilibria are widely available (47). Care must be taken that all species of concern are in the database referenced by the program being used, and if necessary, important species must be added in order to get the complete picture. 

Some results of application of theoretical models to trace metal speciation were presented in the section on metal-inorganic interactions (tables 2 and 3) a collection of papers dealing with chemical modelling in aqueous systems, including speciation, sorption, solubility and kinetics was edited by 3enne (1979). Recently Nordstrom and Ball (198 0 summarized 58 aqueous chemical equilibrium computer programs of which 19 were dealing with trace metals. 

Mouvet C. and Bourg A. C. M. (1983) Speciation (including adsorbed species) of copper, lead, nickel, and zinc in the Meuse River observed results compared to values calculated with a chemical equilibrium computer program. Water Res. 6, 641-649. 

To calculate sulfur emissions, an equation for gas-slag chemical equilibrium for sulfur (Equation 2) and a mass balance for sulfur are solved simultaneously. First, the equilibrium gas compositions were calculated for the combustion of coal with air for a range of sulfur concentrations in the coal. This was done using Alcoa s Chemical Equilibrium Computer Program (23). Next, the concentrations of sulfur in the slags for equilibrium with the combustion gases were calculated. Finally, the quantity of additives needed to obtain these compositions were calculated from sulfur mass balances. 

Chemical equilibrium computations show that complexes formed with the natural organic matter are the dominant Cu species for total dissolved Cu concentrations on the order of or less than the model ligand concentrations. The Cu concentrations used in the complexometric titrations were much higher than the natural Cu concentrations. Therefore, the complexation parameters probably do not provide an accurate estimate of Cu speciation at natural concentrations. Cu complexation would probably be underestimated at natural Cu concentrations. 

Seider, W. D., R. Gautam, C. W. White, 1980, Computation of Phase and Chemical Equilibrium. Computer Applications to Chemical Engineering, ACS Symposium Series 124, p. 115-13... 

Reactions of metal ions in aqueous media have been show n to be strongly influenced by surface sorption reactions. The adequate description of metal ion behavior in systems where particulates have been included is an important step in the application of laboratory data to natural systems of wide environmental interest. In this study, data on the adsorption of aqueous nickel, Ni, onto oxides of silica and iron is presented. Of special interest are the effects which various ligands have on the adsorption reactions. Data are analyzed through the use of the chemical equilibrium computer model REDEQL2 making use of the solvent-ion model of adsorption. 

A12. ingle, S.B., J.A. Kenistonand D.W. Schulta. "REDEQL.BPA Aqueous Chemical Equilibrium Computer Program", EPA Report EPA-600/3-80 049 (1980)... 

AG Varias, JL Feng, Simulation of hydride induced steady-state crack growth in metals - Part I Growth near hydrogen chemical equilibrium. Computational Mechanics, 2004, 34, 339-356. 

S. Gordon and B. J. McBride, "Computer Program for Calculation of Complex Chemical Equilibrium Composition, Rocket Performance, Incident and Reflected Shocks, and Chapman-Jouget Detonations," NASA SP-273, Interim Revision, NTIS, Springfield, Va., Mar. 1976. 

Another general type of behavior that occurs in polymer manufacture is shown in Figure 3. In many polymer processing operations, it is necessary to remove one or more solvents from the concentrated polymer at moderately low pressures. In such an instance, the phase equilibrium computation can be carried out if the chemical potential of the solvent in the polymer phase can be computed. Conditions of phase equilibrium require that the chemical potential of the solvent in the vapor phase be equal to that of the solvent in the liquid (polymer) phase. Note that the polymer is essentially involatile and is not present in the vapor phase. 

Even if a system is not in chemical equilibrium it is possible to calculate the rate at which it is approaching equilibrium if we have sufficiently detailed knowledge of the energies involved in the transition state (so that it is possible to calculate the partition functions - the crucial step). However, computational chemistry has advanced to a level that good estimates of reaction rates can almost be obtained routinely. We will discuss examples in Chapter 6. 

Several workers have intended to estimate the chemical compositions of Kuroko ore fluids based on the chemical equilibrium model (Sato, 1973 Kajiwara, 1973 Ichikuni, 1975 Shikazono, 1976 Ohmoto et al., 1983) and computer simulation of the changes in mineralogy and chemical composition of hydrothermal solution during seawater-rock interaction. Although the calculated results (Tables 1.5 and 1.6) are different, they all show that the Kuroko ore fluids have the chemical features (1 )-(4) mentioned above. 

More than 50 computer codes that calculate chemical equilibrium in natural waters or similar aqueous systems are described in the literature.122 Most are not suitable for modeling the deep-well... 

When the simulation of deep-well temperatures, pressures, and salinities is imposed as a condition, the number of codes that may be of value is reduced to a much smaller number. Nordstrom and Ball121 recommend six references as covering virtually all the mathematical, thermodynamic, and computational aspects of chemical-equilibrium formulations (see references 123-128). Recent references on modeling include references 45, 63, 70, 129, and 130. 

Detonation pressure and temperature of hydrogen-air mixtures starting from 101.3 kPa (1 atm) and 298 K (25°C). Chapman-Jouguet calculations using the Gordon-McBride code. (After Gordon, S. and McBride, B.J., Computer Program for Calculation of Complex Chemical Equilibrium Compositions and Applications, NASA Reference Publication, Cleveland, Ohio, 1994.)... 

Computer Program for Calculation of Complex Chemical Equilibrium Compositions and Applications, NASA Reference Publication, Cleveland, Ohio, 1994.)... 

Parker, D.R., W. A. Norvell and R. L. Chaney, 1995, GEOCHEM-PC, a chemical speciation program for IBM and compatible personal computers. In R. H. Loep-pert, A. P. Schwab and S. Goldberg (eds.), Chemical Equilibrium and Reaction Models. Soil Science Society of America Special Publication 42,253-269. 

Schecher, W. D. and D.C. McAvoy, 1994, MINEQL+, A Chemical Equilibrium Program for Personal Computers, User s Manual, version 3.0. Environmental Research Software, Inc., Hallowell, ME. 

Tipping E., 1994, WHAM - a chemical equilibrium model and computer code for waters, sediments and soils incorporating a discrete site/electrostatic model of ion-binding by humic substances. Computers and Geosciences 20,973-1023. 

Westall, J. C., J. L. Zachary and F. F. M. Morel, 1976, Mineql, a computer program for the calculation of chemical equilibrium composition of aqueous systems. Technical Note 18, R. M. Parsons Laboratory, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA. 

Although several examples implementing the Newton-Raphson method for the computation of chemical equilibrium are developed in Chapter 6, we will now present some simple applications that illustrate its basic principles. 

Exp-6 potential models can be validated through several independent means. Fried and Howard33 have considered the shock Hugoniots of liquids and solids in the decomposition regime where thermochemical equilibrium is established. As an example of a typical thermochemical implementation, consider the Cheetah thermochemical code.32 Cheetah is used to predict detonation performance for solid and liquid explosives. Cheetah solves thermodynamic equations between product species to find chemical equilibrium for a given pressure and temperature. From these properties and elementary detonation theory, the detonation velocity and other performance indicators are computed. 

Westall, J. "FITEQL. A Computer Program for Determination of Chemical Equilibrium constants from Experimental Data,"... 

Whatever the aim of a particular titration, the computation of the position of a chemical equilibrium for a set of initial conditions (e.g. total concentrations) and equilibrium constants, is the crucial part. The complexity ranges from simple 1 1 interactions to the analysis of solution equilibria between several components (usually Lewis acids and bases) to form any number of species (complexes). A titration is nothing but a preparation of a series of solutions with different total concentrations. This chapter covers all the requirements for the modelling of titrations of any complexity. Model-based analysis of titration curves is discussed in the next chapter. The equilibrium computations introduced here are the innermost functions required by the fitting algorithms. 

A chemical model has been developed that predicts equilibria for wet scrubbing of S02 by limestone slurry, with magnesia additive to enhance S02 removal. The model is implemented by an equilibrium computer program. 

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