Dissociation reactions, reversible

However, as the temperature of the flue gas decreases, as heat is extracted, the dissociation reactions reverse and the heat is released. Thus, although theoretical flame temperature does not reflect the true flame temperature, it does provide a convenient reference to indicate how much heat is actually released by combustion as the flue gas is cooled. Figure 15.21 shows the flue gas starting from the theoretical flame temperature. This is cooled... 

The reverse of reaction 6.15 is called a dissociation reaction and is characterized by a dissociation constant, Ka, which is the reciprocal of K. ... 

Enzyme inhibitors are classified in several ways. The inhibitor may interact either reversibly or irreversibly with the enzyme. Reversible inhibitors interact with the enzyme through noncovalent association/dissociation reactions. In contrast, irreversible inhibitors usually cause stable, covalent alterations in the enzyme. That is, the consequence of irreversible inhibition is a decrease in the concentration of active enzyme. The kinetics observed are consistent with this interpretation, as we shall see later. 

Activation energy values for the recombination of the products of carbonate decompositions are generally low and so it is expected that values of E will be close to the dissociation enthalpy. Such correlations are not always readily discerned, however, since there is ambiguity in what is to be regarded as a mole of activated complex . If the reaction is shown experimentally to be readily reversible, the assumption may be made that Et = ntAH and the value of nt may be an indication of the number of reactant molecules participating in activated complex formation. Kinetic parameters for dissociation reactions of a number of carbonates have been shown to be consistent with the predictions of the Polanyi—Wigner equation [eqn. (19)]. 

Since the synthesis temperatures are higher than the dissociation temperatures of the phases that are formed (at a pressure of lO N m ), it is necessary to react the alkali metal with boron under metal pressure in excess of that defined by Eq. (a), in sealed vessels. The alkali metal is present as a liquid in equilibrium with the vapor phase, the pressure of which is determined by the T of the coldest point. This pressure (greater the more volatile the metal) favors the synthetic reaction relative to the reverse dissociation reaction. 

Let us now consider the the reverse of the binary complex dissociation reaction that we just described. We now turn our attention to the kinetics of association between an enzyme molecule and a ligand. The association reaction is described as follows ... 

Let us combine the association and dissociation reactions that we have discussed above to describe the whole system of reversible ligand interactions with an enzyme ... 

Because association is reversed by the dissociation reaction, one does not ever achieve complete conversion of free E and I to the El complex. Rather, the system approaches an equilibrium with respect to the concentrations of E, /, and EL We can define an equilibrium association constant as the ratio of products to reactants, or as the ratio of the forward to reverse rate constants ... 

The rate equation for the reversible reaction of E and I must reflect both the forward (association) and reverse (dissociation) reactions ... 

For other electrolytes, now termed weak, factor i has non-integral values depending on the overall electrolyte concentration. This fact was explained by Arrhenius in terms of a reversible dissociation reaction, whose equilibrium state is described by the law of mass action. 

A The dissociation reaction is the reverse of the formation reaction and thus AG for the dissociation reaction is the negative of AG°f... 

Kinetic parameters for forward and reverse complexation and dissociation reactions ... 

Chloride substitution kinetics of [NiniL(H20)2]3+, and its protonated form [NiniL(H20)(H30)]4+, where L = 14 -oxa-1,4,8,11 -tetraazabicy-clo[9.5.3]nonadecane, yield fyn20)2 = 1400 M 1s 1 and (h2o)(H3o+) = 142M 1s V The reverse, chloride dissociation, reactions have (h2o)ci = 2.7 s 1 (h3o+)ci = 0.22 s All four reactions occur through dissociative interchange mechanisms, like earlier-studied substitutions at nickel(III) (359). 

The above discussion shows that several possible pathways for the interconversion of sulfur rinp exist. However, none of these alone can explain all the experimental observations. It therefore seems likely that several of them are effective simultaneously. Unimolecular dissociation reactions as discussed under (a) and (d) will dominate at high temperatures due to the increase in entropy. At lower temperatures, however, bimolecular reactions like the dimerization (c) may be most important, at least in case of the small rings (Sg, S, Sg) whose unimolecular dissociation is strongly endothermic. Larger rings will probably decompose according to mechanism (d), which in a way is the reversal of the dimerization (c). 

Acids are classified as strong or weak, depending upon their degree of ionization in water. A weak acid ionizes in water reversibly to form HjO ions. A weak acid is a weak electrolyte, and its aqueous solution does not conduct electricity well. The dissociation reaction occurs to a very small extent usually, fewer than 1 percent of the HA molecules are ionized. The ionization of a weak acid is shown as follows ... 

Consider an alternate dissociative adsorption mechanism in which gas-phase A2 adsorbs on a single open site, followed by a separate dissociation reaction of A2(s) into two A(s) species. Assume that both steps are reversible. 

Depending on the pressure, recombination reactions (the reverse of the dissociation reactions) may be bimolecular or termolecular reactions. Recombination of hydrogen atoms is typically at its low-pressure limit and proceeds as a termolecular reaction,... 

As we saw in Section 15.13, the equilibrium constant for a net reaction equals the product of the equilibrium constants for the reactions added. Therefore, we multiply Ka for CH3C02H by the reciprocal of Kw to get Kn for the neutralization reaction. (We use 1 /Kw because the H20 dissociation reaction is written in the reverse direction.) The resulting large value of Kn (1.8 X 109) means that the neutralization reaction proceeds nearly 100% to completion. 

The extension of matrix IET to bulk reversible association-dissociation reactions [282] and reversible excitation binding [283]... 

Reaction 12 is the reverse of the metal-alkyl bond dissociation process (Equation 15). Hence, the activation enthalpies (AH ) of such homolytic bond dissociation reactions are expected to be close to the corresponding bond-dissociation energies. 

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