Chemical-Reaction Equilibria

DR Olander. Simultaneous mass transfer and equilibrium chemical reaction. AIChE J 6 233-239, 1960. 

The influence of equilibrium chemical reactions on vapor-liquid phase diagrams. Chem. Engng. Sci.,... 

S. Ung and M. F. Doherty, Calculation of residue curve maps for mixtures with multiple equilibrium chemical reactions. Ind. Engng. Chem. Res.,... 

Eiev is the open circuit potential of an electrochemical cell in which an equilibrium chemical reaction takes place. 

To solve equations of state, you must solve algebraic equations as described in this chapter. Later chapters cover other topics governed by algebraic equations, such as phase equilibrium, chemical reaction equilibrium, and processes with recycle streams. This chapter introduces the ideal gas equation of state, then describes how computer programs such as Excel , MATLAB , and Aspen Plus use modified equations of state to easily and accurately solve problems involving gaseous mixtures. 

Consider the following equilibrium chemical reaction wherein the reactants are present in stoichiometric proportion ... 

Nonequilibrium transport of solutes through porous media occurs when ground-water velocities are sufficiently fast to prevent attainment of chemical and physical equilibrium. Chemical reactions in porous media often require days or weeks to reach equilibrium. For example. Fuller and Davis Q) reported that cadmium sorption by a calcareous sand was characterized by multiple reactions, including a recrystallization reaction that continued for a period of days. Sorption of oxyanions by metal oxyhydroxides often occurs at an initially rapid rate the rate then decreases until steady-state is achieved (2-4). Unless ground-water velocity in such a situation is extremely slow, nonequilibrium transport will occur. 

We write the general form of an equilibrium chemical reaction as... 

In this paper, we focus on the effect of equilibrium chemical reaction inside the meirbrane. We consider the common reversible reaction of the form... 

Natural water contains numerous different elements, which interact between themselves and tend to some state of equilibrium. Upon reaching equilibrium, chemical reactions acquire reversible nature, at which the rates of opposite processes become equal and the solution s composition does not change. Such a state is called chemical equilibrium. Under stable conditions, any natural water tends to such equilibrium. 

It is also necessary to distinguish between the equilibrium and the steady state (see, e.g. [144, 145]). The latter essentially embraces non-equilibrium chemical reaction processes where reaction rates of only some constituents are zero and do not contribute to the (non-zero) entropy production. 

Barbosa, D., and M.F. Doherty, The Influence of Equilibrium Chemical Reactions on Vapor-Liquid Phase Diagrams, Chem. Eng. ScL, 43, 529 (1988a). 

Perhaps one reason for the non-competitiveness of liquid films as gas separators - besides the difficulties of fabricating ultra-thin porous membranes and preventing their dessication - is that the theoretical aspects of CO transport in alkaline media have not been fully explored. Solutions to the differential equations governing steady-state CO2 diffusion with non-equilibrium chemical reaction are available, and the appreciable effects of catalysts and buffers have been elucidated. However, noteworthy aspects of the equilibrium (fast reaction) regime in simple alkaline solutions have not been fully examined. 

A third concept is introduced when chemical reaction and phase equilibrium phenomena are superimposed in the unit reactive distillation lines. The following sequence of phase equilibrium— chemical reaction steps is adopted for the evolution of reactive distillation lines,... 

From a different and more rigorous perspective, a reactive azeotrope might be characterized by the satisfaction of the following necessary and sufficient conditions for a system undergoing a single equilibrium chemical reaction (Barbosa and Doherty, 19876 ... 

These necessary and sufficient conditions for reactive azeotropes have been generalized and theoretically established for the case of multicomponent mixtures undergoing multiple equilibrium chemical reactions by Ung and Doherty (19956). The starting point for their analysis is the introduction of transformed compositions. It is widely recognized that mole fractions are not the most convenient measures of composition for equilibrium reactive mixtures, as they might lead to distortions in the equilibrium surfaces (Barbosa and Doherty, 1988a Doherty and Buzad, 1992). In order to visualize in a much more... 

When a mixture of nc-components undergoes rirx simultaneous equilibrium chemical reactions, the RCM expression may be described in terms of transformed molar compositions and a reaction-warped time (Ung and Doherty, 1995a),... 

For a reaction at isobaric and isothermal conditions, the affinity A characterizes the distance from equilibrium. Chemical reactions are usually far from global equilibrium. The fuudameutal equation for a chemical... 

Thus, the governing equations (10)-(12) with the first order transport terms describe a flow of reacting mixture of viscous gases with strong non-equilibrium chemical reactions in the Navier-Stokes approximation. Transport properties in the one-temperature approach in reacting gas mixtures are considered in Em Giovangigli (1994) Kustova (2009) Kustova et al. (2008) Nagnibeda Kustova (2009). 

E.9 Phenomenological Theory of Non-equilibrium Chemical Reaction Processes... 

Prior to the teaching of chemical equilibrium, chemical reactions are presented as going to completion, meaning that all reactants are used up and converted into products. If the original amounts of reactants are not stoichiometrically equivalent, then one or more reactants might remain but then certainly one of the reactants is used up. This assumption is strongly reinforced by the kind of classroom work and homework problems given to the students. 

Finally, let us apply LeChatelier s principle to determine the effect of temperature on an equilibrium chemical reaction. Raising the temperature of a system is equivalent to adding heat. Therefore, if the temperature of a system is raised at constant pressure, the chemical reaction will proceed in the direction that absorbs heat (i.e., in the direction of the so-called endothermic reaction). For example, the reverse reaction of Reaction (1.11) is endothermic, but the forward reaction is exothermic (i.e., heat is released by the forward reaction). Therefore, the equilibrium shifts in the forward direction if the temperature is lowered, and in the reverse direction if the temperature is raised at constant pressure. 

Further development of this theory relates the chemical potential to measurable state variables such as p, T and iV. Thus, the pioneering work of De Donder established a clear connection between entropy production and irreversible chemical reactions. In a closed system, if initially the system is not in chemical equilibrium, chemical reactions will take place that irreversibly drive the system towards equilibrium. And, according to the Second Law of thermodynamics, this will happen in such a way that (4.1.10) is satisfied. 

The partition functions, p and q, represent equilibrium chemical reactions for formation of the solute-carrier complex at the external phase-membrane interface and decomposition of the solute-carrier complex at the membrane-internal phase interface, respectively. 

Oxygen-Rich versus Fuel-Rich Fires The distinction between an oxygen-rich or fuel-rich fire is used to describe the state of the fire relative to a nominal or stoichiometric combustion process. In the oxygen-rich state there is sufficient oxygen to allow for, theoretically, complete combustion of the available fuel. Remember that the combustion process is a series of competitive equilibrium chemical reactions therefore, it is fair to assume that not all of the intermediate products will be fully converted in the reaction chain. Growth of a fire in the oxygen-rich state is marked by direct heat transfer from the flame to the additional fuel supply. The exhaust gases mix readily with available fresh air and are cooled and diluted. 

J. M. Anna, C. R. Baiz, M. R. Ross, R. McCanne and K. J. Kubaiych, Ultrafast Equilibrium and Non-Equilibrium Chemical Reaction Dynamics Probed with Multidimensional Infrared Spectroscopy, Int. Rev. Phys. Chem, 2012, 31, 367. 

Overall, heat and water are added to the process to produce H2 and oxygen. Many of the papers presented at this conference describe ongoing research on this process. All other chemical reagents are fully recycled. The first step, the catalytic decomposition of sulfuric acid, is the high-temperature, energy-intensive step. It is an equilibrium chemical reaction that can proceed in either direction. High temperatures and low pressures drive the reaction to the right toward completion. At 10 bars, the reaction is estimated to go to 31% completion at 625 C, 79% completion at 725 C, and 99% completion at 925 C. 

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