Thermodynamically favorable reactions

Unfortunately, the thermodynamically favored reactions of trichlo-rolluoromethane (CFC-11) and dichlorodifluoromethane (CFC-12) with water do not proceed to a significant degree below 300 C and at least 200 atm (1 atm = 101.325 kPa) or greater [42] (equation 44) Even at 4000 atm randoimzation rather than complete hydrolysis occurs, leaving another chlorofluorocarbon, chlorotri-fluoromethane (CFC-13), which is also potentially harmful to the earth s ozone layer... 

A negative AE indicates an exothermic (thermodynamically favorable) reaction, while a positive AE an endothermic (thermodynamically unfavorable) reaction. 

While hydrolysis is a thermodynamically favored reaction, the amide and phosphoester bonds of polypeptides and ohgonucleotides are stable in the aqueous environment of the cell. This seemingly paradoxic behavior reflects the fact that the thermodynamics governing the equihbrium of a reaction do not determine the rate at which it will take place. In the cell, protein catalysts called enzymes are used to accelerate the rate... 

The double arrows indicate reversibifity, an intrinsic property of all chemical reactions. Thus, for reaction (1), if A and B can form P and Q, then P and Q can also form A and B. Designation of a particular reactant as a substrate or product is therefore somewhat arbitrary since the products for a reaction written in one direction are the substrates for the reverse reaction. The term products is, however, often used to designate the reactants whose formation is thermodynamically favored. Reactions for which thermodynamic factors strongly favor formation of the products to which the arrow points often are represented with a single arrow as if they were irreversible ... 

Sulfanes decompose to produce H2S and sulfur in a thermodynamically favored reaction. 

The solid state and the surface chemistry of some of the solid Fe-phases impart to these oxides and sulfides the ability to catalyze redox reactions. Surface complexes and the solid phases themselves acting as semiconductors can participate in photoredox reactions, where light energy is used to drive a thermodynamically unfavorable reaction (heterogeneous photosynthesis) or to catalyze a thermodynamically favorable reaction (heterogeneous photocatalysis). 

A new class of functional comonomers exemplified by acrylamidobutyraldehyde dialkyl acetals 1 and their Interconvertible cyclic hemlamidal derivatives 2 were prepared and their chemistry was Investigated for use In polymers requiring post-crosslInking capability. These monomers do not possess volatile or extractable aldehyde components and exhibit additional crosslinking modes not found with conventional am1de/forma1dehyde condensates, eg, loss of ROH to form enamides 9 or TO and facile thermodynamically favored reaction with diols to form cyclic acetals. 

The relationship between reaction velocity and enzyme concentration (in the absence of self-association of the enzyme) should also be adjusted such that reaction rate is linearly related to catalyst concentration, [Etotai]- Initial rates typically fail to obtain if [Etotai] = 0-01 [Ajmitiai where [Ajinitiai is the initial substrate concentration. As a general rule, the substrate concentration will not have changed more than 5-10% of its value over the initial rate phase of the reaction. This rule-of-thumb applies only to thermodynamically favorable reactions, and investigators are well advised to limit substrate consumption to well below 5%. 

The stability of the charge that is stored is limited by the thermodynamically favored reactions connected with both hydrogen and oxygen evolution [348]... 

As a result, these anions can gain exceptional stability and their carbon acids are unusually acidic. Because the above resonance forms probably play very important roles in stabilizing the anion, these species are not purely carbanions. However, thermodynamics favors reactions (protonation or alkylation) at carbon so their behavior is generally characteristic of carbanions. It also should be noted that kinetics often favor reaction at the heteroatom in these anions though leading to the less stable product. ... 

Another important point is that some thermodynamically favorable reactions (that is, reactions for which AG ° is large and negative) do not occur at meas-... 

Exercise 15-25 The equilibrium for the formation of urea compounds from the hydrolysis of substances called carbodiimides is a thermodynamically favorable reaction ... 

Microorganisms have adapted to efficiently harvest energy from kinetically slow but thermodynamically favorable reactions through the continuum of redox potentials found in nature. 

The reaction of 3-mercaptoindole with amidophosphite esters takes place similarly. The author of [11] has evaluated the enthalpies of the reactions at the SH and NH groups of the molecule, but the conclusions about the thermodynamically favorable reaction product need to be revised. 

Undecylenic acid has also been shown to react with the surface preferentially at the alkene end, leaving the terminal carboxylic acid group free for further reaction [53], This result was somewhat unexpected as the Si-H sites are considered to be somewhat acidic and the oxophilic nature of silicon should thermodynamically favor reaction with the hydroxyl group of the acid. The preferential reactivity with the alkenyl end is consistent with a free radical, rather than a nucleophilic mechanism. The acid function can be activated with N-hydroxy succinimide (NHS) to facilitate coupling with amine tagged molecules. Schematically,... 

The thermodynamically favored reaction paths for one- or two-stage oxidation of propene are ... 

Many unstable substances are simply reactive, i.e., kinetically unstable. In recent years a realization of this has led to the design of ligands or substituents that diminish reactivity. Most commonly, this is done simply by placing so much steric hindrance in the potential reaction path that an otherwise thermodynamically favored reaction cannot get underway. In other cases, it is a question of choosing ligands or substituents that are themselves unable to engage in a type of reaction that could result in decomposition. In this section examples of both of these approaches will be presented. 

Hydrido alkyl species L M(H)(R) are particularly prone to elimination of R—H this thermodynamically favored reaction is the reverse of C—H activation (see Section 21-4) and explains why for a long time intermolecular C—H activation remained elusive. For example, the protolysis of (TMEDA)PtMe2 by HC1 does not lead to the direct electrophilic attack of H+ on the Pt—Me bond but gives thermally unstable hydrido alkyl (TMEDA)Pt(H)ClMe2 which undergoes reductive elimination via a coordinatively unsaturated 5-coordinate intermediate 97... 

Effect of Impurities on CaS04 Transformation. The transition from gypsum to orthorhombic anhydrite is slow but occurs even at ambient temperatures (44). The relatively large concentration of finely divided sodium chloride present in the plaster in the tomb of Nefertari may have facilitated the dehydration process. The presence of a hygroscopic material, such as sodium chloride, can help promote dehydration reactions. Also, impurities within the lattice of a crystalline structure can weaken the lattice (46, 47) and thereby accelerate thermodynamically favored reactions. These points suggest a strong correlation between the extent to which the dehydration reaction proceeds and sodium chloride concentration, but they do not exclude the possibility that dehydration can take place in the absence of salt. 

Even for thermodynamically favorable reactions, a large activation energy means that the reaction will be slow. For thermodynamically unfavorable reactions, even a fast reaction (with small activation energy) would be unlikely to occur. The rate of reaction depends on the activation energy, as in the Arrhenius equation... 

A solution containing 0.001 M ubiquinone and 0.001 M ubiquinone-Ha was mixed with an equal volume of a solution containing 0.1 M fumarate and 0.1 M succinate. (a) Write the equation for a thermodynamically favorable reaction that could occur, (b) Calculate the A , AG, and K. values. 

Thermodynamically favorable reactions such as A------> B which suffer from ki-... 

---