FACTORS CAUSING EQUILIBRIUM

It is known that many of the chemical reactions are equilibrium reactions (reversible). 

There are two opposing tendencies causing equilibrium in a chemical reaction  

In nature, matter tends to lose energy to reach a lower energy state. 

In an exothermic reaction, the potential energy of reactants is greater than that of its products. Thus, the tendency toward minimum energy is in favor of its products. 

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Despite this detailed familiarity with equilibrium, there is one facet we have not considered at all. What determines the equilibrium constant Why does one reaction favor reactants and another reaction favor products What factors cause sodium chloride to have a large solubility in water and silver chloride to have a low solubility Why does equilibrium favor the reaction of oxygen with iron to form FejAi (rust) but not the reaction of oxygen with gold As scientists, we cannot resist wondering what factors determine the conditions at equilibrium. 

In this paper we formulated and solved the time optimal problem for a batch reactor in its final stage for isothermal and nonisothermal policies. The effect of initiator concentration, initiator half-life and activation energy on optimum temperature and optimum time was studied. It was shown that the optimum isothermal policy was influenced by two factors the equilibrium monomer concentration, and the dead end polymerization caused by the depletion of the initiator. When values determine optimum temperature, a faster initiator or higher initiator concentration should be used to reduce reaction time. 

Le Chatelier s principle is a compact summary of how different factors influence equilibrium. Introducing a reagent causes a reaction to proceed in the direction that consumes the reagent. Reducing the temperature removes heat from the system and causes the reaction to produce heat by proceeding in the exothermic direction. 

Since K is a concentration equilibrium constant, it is a non-ideal equilibrium constant, and so k is also a non-ideal rate constant, which incorporates all the factors causing non-ideality. Since these factors will be different for different reactions, these rate constants and their derived kinetic parameters should not be used for comparisons of reactions, but must first be converted to ones where the effects of non-ideality have been taken care of, i.e. ideal values. 

One of the factors causing fouling in ultrafiltration membranes is the adsorption of solutes in the membrane pores. Since fouling, in general, has been discussed in the previous chapter, the discussion presented here will be restricted to the adsorption phenomenon. Clark et al. [37] studied the relationship between membrane fouling and protein adsorption on alumina ultrafiltration membranes. Equilibrium adsorption of bovine serum albumin (BSA) was measured by the standard static method at 7°C. Their study covered the concentration range between 1 and 10 g/1, pH values between 2 and 10 and NaCl... 

Temperature affects the equilibrium constants of dissolved inorganic carbon and, in particular, the solubility coefficient of CO2, so that Pco2 rises by 4% with an increase of 1 °C in temperature. In the sampling region, the surface water temperature decreased from the west to the east, similar to that of Pcos (Fig- 4.5). Thus this was another possible factor causing the Pco2 distribution to show such a pattern in this study. 

We have identified three factors that influence the rate of a chemical reaction. In relating these factors to equilibrium considerations, we will examine only concentration and temperature. These variables affect forward and reverse reaction rates differently. A catalyst, on the other hand, has the same effect on both forward and reverse rates. Therefore, a catalyst does not alter chemical equilibrium. A catalyst does cause a system to reach equilibrium more quickly. 

Mixtures of components, that caimot be physically separated but whose molar fractions can be changed under a number of factors are considered as undefined. Such mixtures cannot be analyzed by means of classical spectrophotometric analysis (lack of calibration as shown above) and tautomeric mixtures are a typical example. Therefore, there are two approaches to treat tautomeric mixtures presented as a set of spectra with different tautomeric ratios direct quantitative analysis based on overlapping band decomposition or nonlinear optimization based on existing physical relations between the tautomeric constant and the external factor causing the shift in the equilibrium. The first one is the only option to analyze changes caused by the solvent or by salt addition. Both could be used to estimate the effects of temperature, acidity, or concentration and a critical comparison is available in Section 2.2.3 in this respect... 

The method was then extended to a multicomponent, undefined mixture [28-30] assuming independence of the individual spectra from the factor causing shift in the position of the tautomeric equilibrium. This assumption allows simultaneous... 

Under certain conditions, it will be impossible for the metal and the melt to come to equilibrium and continuous corrosion will occur (case 2) this is often the case when metals are in contact with molten salts in practice. There are two main possibilities first, the redox potential of the melt may be prevented from falling, either because it is in contact with an external oxidising environment (such as an air atmosphere) or because the conditions cause the products of its reduction to be continually removed (e.g. distillation of metallic sodium and condensation on to a colder part of the system) second, the electrode potential of the metal may be prevented from rising (for instance, if the corrosion product of the metal is volatile). In addition, equilibrium may not be possible when there is a temperature gradient in the system or when alloys are involved, but these cases will be considered in detail later. Rates of corrosion under conditions where equilibrium cannot be reached are controlled by diffusion and interphase mass transfer of oxidising species and/or corrosion products geometry of the system will be a determining factor. 

The third factor that strongly affects the equilibrium between hexa- and heptacoordinated complexes (85) is the nature of the second, outer-sphere cations. Increasing the ionic radii of the cations causes the equilibrium in Equation (85) to shift to the left, forming mostly hexacoordinated complexes MeF6 The mechanism of interionic equilibrium in fluoride melts can be presented schematically as follows ... 

This ease with which we can control and vary the concentrations of H+(aq) and OH (aq) would be only a curiosity but for one fact. The ions H+(aq) and OH (aq) take part in many important reactions that occur in aqueous solution. Thus, if H+(aq) is a reactant or a product in a reaction, the variation of the concentration of hydrogen ion by a factor of 1012 can have an enormous effect. At equilibrium such a change causes reaction to occur, altering the concentrations of all of the other reactants and products until the equilibrium law relation again equals the equilibrium constant. Furthermore, there are many reactions for which either the hydrogen ion or the hydroxide ion is a catalyst. An example was discussed in Chapter 8, the catalysis of the decomposition of formic acid by sulfuric acid. Formic acid is reasonably stable until the hydrogen ion concentration is raised, then the rate of the decomposition reaction becomes very rapid. 

A different melting point, and hence supercooling, is predicted for the strained sector. This is the basis for a different interpretation of the (200) growth rates a regime //// transition occurs on (110) but not on (200). This is despite the fact that the raw data [113] show a similar change in slope when plotted with respect to the equilibrium dissolution temperature (Fig. 3.15). It is questionable whether it is correct to extrapolate the melting point depression equation for finite crystals which is due to lattice strain caused by folds, to infinite crystal size while keeping the strain factor constant. 

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