Chemical equilibrium expression

Tables 13-1, 13-2, and 13-4 include data on formic acid and acetic acid, two substances that tend to dimerize in the vapor phase according to the chemical-equilibrium expression...

Some chemical reactions are reversible and, no matter how fast a reaction takes place, it cannot proceed beyond the point of chemical equilibrium in the reaction mixture at the specified temperature and pressure. Thus, for any given conditions, the principle of chemical equilibrium expressed as the equilibrium constant, K, determines how far the reaction can proceed if adequate time is allowed for equilibrium to be attained. Alternatively, the principle of chemical kinetics determines at what rate the reaction will proceed towards attaining the maximum. If the equilibrium constant K is very large, for all practical purposes the reaction is irreversible. In the case where a reaction is irreversible, it is unnecessary to calculate the equilibrium constant and check the position of equilibrium when high conversions are needed. 

Table 16-2 List of input components for the simplest case of the acid-base balance of unpolluted marine clouds. Also shown are the mass conservation statements, chemical equilibrium expressions and constants, and the requirement for charge balance...

In a similar approach McCall et al.(5) have defined a model ecosystem which represents a unit world, however, this development incorporates standard chemical equilibrium expressions into a... 

The method of using fugacity calculations will be discussed later in this symposium, therefore a detailed description will not be given in this paper. The description of equilibrium models using chemical equilibrium expressions will be discussed with the recognition that the two approaches are very much the same. 

By using the fundamental. principles of conservation of mass and charge, and chemical equilibrium expressions, the concentration of individual species in solution (sometimes called the "species distribution") can be calculated. The available equilibrium models for lime or limestone based FGD are the Bechtel-modified Radian equilibrium program (BMREP) (4) and the species distribution model (SDM)... 

Since chemical equilibrium expressions involve fugacity coefficients, rather than K-values, it is necessary to introduce a new set of outside loop variables. The K-value is factored as follows ... 

The equations required to describe this column are developed in the order in which they are solved sequentially in the proposed calculational procedure. On the basis of assumed temperature and L/V profiles, the material balances, the physical equilibrium relationships, and the chemical rate expressions (or chemical equilibrium expressions) are solved for the moles of each component which reacts per stage per unit time and for the component-flow rates. A formulation of the Newton-Raphson method is used. 

Thus, any approach has to consider in principle both contributions the chemical, nonelectrostatic, or intrinsic contribution, and the electrostatic one. Now, to model ion sorption to soil colloidal particles, two main approaches exist chemical modeling (should not be confused with the chemical contribution mentioned in the preceding discussion) and adsorption modeling in the first case, the sorption is treated as a chemical reaction, with the free surface sites considered as a reactant, and a chemical equilibrium expression in terms of the bulk activities is written. In adsorption modeling, an appropriate adsorption isotherm is employed however, it is not written in terms of the bulk activity a, of the adsorbate, but instead it should be related to the activity at the outer Helmholtz plane a, 2> is, at the limit of the diffuse double layer, X2 in Figure 11.1 (see also Section 3.3.3). Both are related, due to the condition of constancy of the electrochemical potential (Section 3.1.1), by... 

Once the value of the equilibrium constant is known, the equilibrium-constant expression can be used to calculate concentrations of reactants or products at equilibrium. Suppose an equilibrium system at 425°C is found to contain 0.015 mol/L each of H2 and I2. To find the concentration of HI in this system, rearrange the chemical equilibrium expression as shown in the two equations that follow. 

Write the chemical equilibrium expression for the following reaction ... 

Notice that is the product of the molar concentration of Ca + ions and the molar concentration of F ions squared, as required by the balanced chemical equilibrium expression. 

The minimum amount required to achieve complete conversion of the hydrocarbon feedstock is 0.5 mol 02 per mol carbon. Steam is added to control the reaction temperature, which leads to additional H2 generation via CO shift [Eq. (3)]. The final partial oxidation effluent gas composition is governed by the following chemical equilibrium expressions ... 

The third important discovery in molecular hydrogen storage was the reversible uptake of hydrogen by lithium nitride LisN by Chen in 2002 [40]. Chen points out in her initial paper that LiNs and H2 were known to generate a ternary Li-N-H species for nearly a century, but the reverse reaction had not been considered earlier. A simple series of chemical equilibrium expressions account for the behavior of the system ... 

Building on earlier related efforts, Trapp (2007) developed a mechanistic model to predict uptake of neutral organic chemicals from soil and air into fruits. A more recent version has been described by Legind and Trapp (2009) and Trapp and Legind (2009). The 2007 model includes eight compartments (two soil compartments, fine roots, thick roots, stem, leaves, fmits, and air) with defined chemical equilibrium expressions, advective transport rates in xylem and phloem, diffusive exchange to soil and air, and growth dilution as the main processes considered. An example data... 

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