Thermodynamic Prediction

Rate coefficients and thermodynamic quantities are connected via equilibrium constant s. For the elementary reaction 

Identifying the concentration product ratio [C]g[D]g/[A]g[B]g with the equilibrium constant expressed in terms of concentrations, we can rearrange Eq. (2.2) to 

This fundamental relation is a form of the principle of detailed balancing. It allows us to relate the rate-coefficient ratio to thermodynamic quantities. 

Equations (2.6) and (2.8) can be used to calculate the Arrhenius parameters for the reverse reaction (A and from measurements of Af and, and vice versa. This is the reason why accurate thermodynamic data for reactive species are an essential prerequisite for modeling the kinetics of reactions where both forward and reverse directions of the same elementary reaction occur. This is particularly so in high-temperature combustion, where many reactions—even those with large AH values—proceed close to equilibrium conditions. 

Let us note two predictions that can be derived for the temperature dependence of the Arrhenius parameters A and E  

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Whenever energy is transformed from one form to another, an iaefficiency of conversion occurs. Electrochemical reactions having efficiencies of 90% or greater are common. In contrast, Carnot heat engine conversions operate at about 40% efficiency. The operation of practical cells always results ia less than theoretical thermodynamic prediction for release of useful energy because of irreversible (polarization) losses of the electrode reactions. The overall electrochemical efficiency is, therefore, defined by ... 

Pourbaix diagrams are only thermodynamic predictions and yield no information about the kinetics of the reactions involved nor are the influences of other ionic species which may be present in the solution included. Complexing ions, particularly haUdes, can interfere with passivation and can influence... 

In oxygenated seawater, uranium is thermodynamically predicted to be present in a hexavalent (-b 6) oxidation state, but it can also exist as the tetravalent U(IV) if conditions are sufficiently reducing. Reduced uranium in the +A oxidation state is highly insoluble or particle reactive. In contrast, U(VI) is readily soluble due to the rapid formation of stable inorganic carbonate complexes. According... 

The electrodeposition of tellurium and silver has been investigated in dilute aqueous solutions of tellurous acid and Ag " ions (concentrations in the order of 10 to 10 " M) in 0.1 M HCIO4 [164], In particular, cyclic voltammetry experiments were conducted with rotating glassy carbon disk electrodes in baths with various concentration ratios of Ag(I) and Te(IV) precursors, and their outcome was discussed in terms of the voltammetric features. For a Ag(I)/Te(IV) ratio close to 0.8, formation of quasi pure silver telluride, Ag2Te, was reported. The authors, based on their measurements and on account of thermodynamic predictions, assumed that silver is deposited first on the electrode (Ag" + e Ag), and then Te(IV) is reduced on the previous silver deposit with formation of Ag2Te according to the reaction... 

Catalysis opens reaction pathways that are not accessible to uncatalysed reactions. It should be self-evident that thermodynamics predict whether a reaction can occur. So, catalysis influences reaction rates (and as a consequence selectivities), but the thermodynamic equilibrium still is the boundary. Catalysis plays a key role in chemical conversions, although it is fair to state that it is not applied to the same degree in all sectors of the chemical industry. While in bulk chemicals production catalytic processes constitute over 80 % of the industrially applied processes, in fine chemicals and specialty chemicals production catalysis plays a relatively modest role. In the pharmaceutical industry its role is even smaller. It is the opinion of the authors that catalysis has a large potential in these areas and that its role will increase drastically in the coming years. However, catalysis is a multidisciplinary subject that has a lot of aspects unfamiliar to synthetic chemists. Therefore, it was decided to treat catalysis in a separate chapter. 

Temperature according to thermodynamics prediction, nickel oxide is reducible by hydrogen at all practical temperatures. However, this heterogeneous reaction,... 

M Marchetti, S Prager, EL Cussler. Thermodynamic predictions of volume changes in temperature-sensitive gels. 1. Theory. Macromolecules 23 1760-1765, 1990. 

Although the formation of a large number of metastable materials that are far from equilibrium cannot be explained thermodynamically, thermodynamics predicts that they will with time transform to the stable phase or phase mixture, often via intermediate phases. More than one hundred years ago, Ostwald pointed out that... 

Thermodynamics predicts under which conditions a catalyst can be reduced. As with every reaction, the reduction will proceed when the change in Gibbs free energy, AG, has a negative value. Equation (2-2) shows how AG depends on pressures and temperature ... 

Thermodynamics Predicts How Confinement Modifies Hard-Sphere Dynamics. 

Despite that thermodynamics predicts the coexistence of molecular Ag+ and PdO oxide particles over a rather large pH domain, AgOH is readily formed at 5 < pH < 13. 

Electrochemical thermodynamics predicts that an anodic reaction may proceed only at electrode potentials more positive than the equilibrium potential of the reaction and a cathodic reaction may proceed only at electrode potentials more negative than the equilibriiun potential. In other words, the Fermi level of the electrode must be higher for the cathodic reaction to proceed and must be lower for the anodic reaction to proceed than the Fermi level of the reaction. 

Hailing, P.J., Thermodynamic predictions for biocatalysis in nonconventional media theory, tests, and recommendations for experimental design and analysis. Enzyme Microb. TechnoL, 1994,16, 178-206. 

The thermodynamic predictions presented in Figure 7.8b indicate that at equilibrium, nitrate should be the dominant form of nitrogen in oxic seawater. This is not observed. Rather, nitrate is the second most abundant nitrogen species, with N2 being 100 times more abundant in surfece seawater and 25 times more abundant in the deep sea. 

Nonideal Physicochemical behavior that does not conform to ideal thermodynamic predictions. 

A beauty of thermodynamics is that it is not concerned with the detailed processes, and its predictions are independent of such details. Thermodynamics predicts the extent of a reaction when equilibrium is reached, but it does not address or care about reaction mechanism, i.e., how the reaction proceeds. For example, thermodynamics predicts that falling tree leaves would decompose and, in the presence of air, eventually end up as mostly CO2 and H2O. The decomposition could proceed under dry conditions, or under wet conditions, or in the presence of bacteria, or in a pile of tree leaves that might lead to fire. The reaction paths and kinetics would be very different under these various conditions. Because thermodynamics does not deal with the processes of reactions, it cannot provide insight on reaction mechanisms. 

Silicon carbide grains are known to contain subgrains of titanium carbide. Equilibrium thermodynamics predicts that titanium carbide will condense before silicon carbide (Fig. 5.13). The titanium carbide grains were apparently accreted by the growing silicon carbide grains and were enclosed as the silicon carbide grains continued to grow. 

The bacterium Klebsiella pneumonia can use quinic acid as a carbon source for its growth the first step here is oxidation of quinic acid to 3-deoxyhydroquinate (DHQ), which is catalyzed by the enzyme quinic acid dehydrogenase. Actually, thermodynamics predicts that the reverse reaction is favored. So if a second bacterium, which made DHQ, had inserted into it the gene for the dehydrogenase, and if this second bacterim did not normally metabolize quinic acid, then this would result in the second organism synthesizing quinic acid from DHQ. 

Life should be so easy We have just made a thermodynamic prediction. If the system comes to equilibrium, we can achieve the desired separation. However, occasionally one substance coprecipitates with the other. In coprecipitation, a substance whose solubility is not exceeded precipitates along with another substance whose solubility is exceeded. For example, some Pb2+ might become adsorbed on the surface of the Hg2I2 crystal or might even occupy sites within the crystal. Our calculation says that the separation is worth trying. However, only an experiment can show whether or not the separation actually works. 

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