Reaction direction equilibrium

The reaction does not feature a bimolecular step, such as direct Sn2 attack of the hydroxide nucleophile on the cobalt center. Rather, hydroxide ion participates in a prior-equilibrium reaction, and the actual rate-controlling reaction is believed to be the uni-molecular expulsion of the leaving group from a species that contains a coordinated... 

Ester alcoholysis (transesterification) in organic media is an equilibrium reaction and must be shifted in the desired direction. For example, Bornscheuer and coworkers [61] reported the resolution of ibuprofen vinyl ester by transesterification tvith n-hexanol in the presence of CAL-B. The vinyl alcohol generated during the reaction tautomerizes to acetaldehyde, thus making the reaction irreversible, as illustrated in Figure 6.14. 

Transesterification is catalyzed by acids or bases, or performed under neutral conditions. It is an equilibrium reaction and must be shifted in the desired direction. In many cases, low-boiling esters can be converted to higher boiling ones by the distillation of the lower boiling alcohol as fast as it is formed. Reagents used to catalyze transesterification include In/l2, Montmorillonite KlOclay, Ti(OEt)4, Cu(N03)2, which with ethyl acetate is elective for primaiy alcohols, ... 

This type of metallic exchange is used much less often than 12-32 and 12-33. It is an equilibrium reaction and is useful only if the equilibrium lies in the desired direction. Usually the goal is to prepare a lithium compound that is not prepared easily in other ways, for example, a vinylic or an allylic lithium, most commonly from an organotin substrate. Examples are the preparation of vinyllithium from phenyl-lithium and tetravinyltin and the formation of a-dialkylamino organolithium compounds from the corresponding organotin compounds ... 

For a reaction at equilibrium, the rate of the forward reaction is balanced exactly by the rate of the reverse reaction. For this reason, any equilibrium reaction can be written in either direction. The equilibrium constant for the Flaber synthesis of ammonia, for example, can be expressed in two ways ... 

The direction chosen for the equilibrium reaction Is determined by convenience. A scientist interested in producing ammonia from N2 and H2 would use f. On the other hand, someone studying the decomposition of ammonia on a metal surface would use eq,r Either choice works as long as the products of the net reaction appear in the numerator of the equilibrium constant expression and the reactants appear in the denominator. Example applies this reasoning to the iodine-triiodide reaction. 

In addition to defined standard conditions and a reference potential, tabulated half-reactions have a defined reference direction. As the double arrow in the previous equation indicates, E ° values for half-reactions refer to electrode equilibria. Just as the value of an equilibrium constant depends on the direction in which the equilibrium reaction is written, the values of S ° depend on whether electrons are reactants or products. For half-reactions, the conventional reference direction is reduction, with electrons always appearing as reactants. Thus, each tabulated E ° value for a half-reaction is a standard reduction potential. 

Figure 220. Reaction direction from a state (A) to an equilibrium state (B) in a reaction of MgO/H20...

As the number of pores in the gas-permeable membrane are plenty, therefore, an equilibrium is established. Evidently, the carbon-dioxide present in the pores is in direct contact with the internal-electrolyte solution (F), thereby giving rise to a second equilibrium reaction that may be represented as follows ... 

Intuitively, one knows that this equilibrium reaction will proceed to the right to form A1203 and release heat. What largely determines the direction is the free energy change of the reacting system ... 

When you see two arrows that point in opposite directions in a chemical equation, the reaction can proceed in both directions. This type of reaction is called an equilibrium reaction. You will learn more about equilibrium reactions in Unit 4. 

This diagram shows how Qc and Ko determine reaction direction. When Qc < Kc, the system attains equilihrium by moving to the right, favouring products. When Qc = Kc, the system is at equilihrium. When Q, > Kc, the system attains equilibrium by moving to the left, favouring reactants. 

This dissociation is an equilibrium reaction because it proceeds in both directions. Acetic acid is weak, so only a few ions dissociate. The position of equilibrium lies to the left, and the reverse reaction is favoured. In the reverse reaction, the hydronium ion gives up a proton to the acetate ion. Thus, these ions are an acid and a base, respectively, as shown in Figure 8.3. The acid on the left (CH3COOH) and the base on the right (CHsCOO") differ by one proton. They are called a conjugate acid-base pair. Similarly, H2O and are a conjugate acid-base pair. 

Kinetic smdies of the iodination of benzene and acetanilide by iodine, diiodine pentoxide, and sulfuric acid in acetic acid indicate that benzene is involved in an equilibrium reaction prior to the rate-limiting <7-complex formation." It is proposed that this equilibrium involves the formation of a itt-complex between iodine adsorbed on diiodine pentoxide and the benzene as it is adsorbed. In the case of acetanilide the a-complex is formed directly with activated iodine adsorbed on the diiodine pentoxide. 

The large and negative value for hexokinase indicates that this enzyme catalyses the reaction only in the direction of glucose 6-phosphate formation, i.e. it is a non-equilibrium reaction in vivo. In contrast, the low value for phosphoglucoisomerase indicates that it is a reaction that is close to equilibrium in vivo, that is, it can proceed in either direction. AG valnes for all the reactions of glycolysis indicate that those catalysed by hexokinase, phosphorylase, phos-phofractokinase and pyrnvate kinase are non-eqnilibrinm the others are near eqnilibrinm (Fignre 2.6). 

Immediately after the passage of an action potential, the Na ion channels close spontaneously and cannot be re-opened for a period of time. This is the refractory period. An action potential therefore cannot proceed in the opposite direction, i.e. it is unidirectional, which imposes a direction on propagation of the whole action potential. This is analogous to the means by which directionality is achieved in a metabolic pathway or a signalling sequence of reactions within either process there is at least one irreversible (non-equilibrium) reaction which provides directionality (Chapter 2). 

In any signalling process, it is essential that the signal travels only in one direction (e.g. action potential in a nerve, signalling in hormone action). To do this, non-equilibrium reactions must be included in the sequence. 

Various combinations of reactant(s) and process conditions are potentially available to synthesize polyesters [Fakirov, 2002 Goodman, 1988], Polyesters can be produced by direct esterification of a diacid with a diol (Eq. 2-120) or self-condensation of a hydroxy carboxylic acid (Eq. 2-119). Since polyesterification, like many step polymerizations, is an equilibrium reaction, water must be continuously removed to achieve high conversions and high molecular weights. Control of the reaction temperature is important to minimize side reactions such as dehydration of the diol to form diethylene glycol... 

Exchangers that have been loaded with cations or anions can be regenerated by treatment with acid or alkali, respectively, since one is always dealing with an equilibrium reaction. Commercially available ion exchangers are frequently delivered in the form of salts so that before use they must be converted into the free acids or bases. Metal cations can also be directly exchanged with one another. 

The cyclic characteristic C is small in the vicinity of thermodynamic equilibrium. We can find the overall reaction rate approximation in the vicinity of equilibrium either directly from kinetic polynomial or by expanding the reaction rate in power series by the small parameter C. The explicit expression for the first term is presented by Lazman and Yablonskii (1988, 1991). It is written as follows ... 

The reactivation is an equilibrium reaction. Under some conditions—e.g., when the oxime reacts directly with the organophosphate ester (Reaction 3) or when the equilibrium constant is less than 1 (Reaction 2)—the phosphorylated oxime can inhibit the enzyme by driving the reaction to the left. 

If the tendencies toward minimum energy and maximum randomness are in favor of opposite directions in a reaction, the reaction becomes an equilibrium reaction. 

If the tendency toward minimum energy and maximum randomness both favor the same direction, the reactions are not reversible. Which of the following reactions is riQt an equilibrium reaction ... 

The net cell reaction is an equilibrium reaction. The cell voltage directly relates to the spontaneity of a reaction. The effect of concentration on cell voltages can easily be explained by Le ChMelier s principle. Let us consider the following reaction ... 

In order to determine the products of decomposition for equilibrium reactions the Kistiakowsky-Wilson or the Springall Roberts rules can be applied as a starting point. From the products of decomposition the heat and temperature of explosion can then be calculated. The temperature of explosion can then be used to calculate the products of decomposition. In practice, this process is repeated many times until there is agreement between the answers obtained. Equilibria of complex reactions and of multi-component systems are today obtained by computer however, the ability to use tabulated data is useful in predicting the direction and extent of the reaction. 

Consider a reversible reaction with a ArG° value of-20 kJ mol-1. In which direction will this reaction occur at the point at which the reaction quotient, Qn is 1000 What is the equilibrium reaction constant, KT, of this reaction ... 

The facts that have just been described lend considerable support to the Lindemann theory. If this theory is to be applicable, the rate of activation and deactivation at higher pressures ought to be great compared with the rate of chemical change, in order that there may be little disturbance of the statistical equilibrium and hence an absolute rate of reaction directly proportional to the total concentration. At first some difficulty was felt about this point, but the solution appears to have been found, and indeed the solution itself constitutes a rather strong piece of evidence in favour of the theory. 

Much information can be gained by examining trends in redox potentials within series of compounds. Let us consider such a series of coordination compounds, M0, Mj, M2. .. M , which undergo reversible, one-electron oxidation reactions at potentials E°0, E°lf E°2,... E° respectively, with respect to the same reference electrode. If we define the oxidation of M0 as our standard reaction (equation 8), then we can examine the variation of the free energy difference, F(E°0— E° ), in terms of the structural difference between M0 and each other member M . Such an analysis is directly comparable to the classic approach of Hammett17 which relates a free energy difference term, log(AH/Ax), for equilibrium reactions such as (9) and (10), to the nature of the aryl substituent, X. 

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