Oxidation-reduction reactions disproportionation

Chemically, nonmetals are usually the opposite of metals. The nonmetallic nature will increase towards the top of any column and toward the right in any row on the periodic table. Most nonmetal oxides are acid anhydrides. When added to water, they will form acids. A few nonmetals oxides, most notably CO and NO, do not react. Nonmetal oxides that do not react are neutral oxides. The reaction of a nonmetal oxide with water is not an oxidation-reduction reaction. The acid that forms will have the nonmetal in the same oxidation state as in the reacting oxide. The main exception to this is N02, which undergoes an oxidation-reduction (disproportionation) reaction to produce HN03 and NO. When a nonmetal can form more than one oxide, the higher the oxidation number of the nonmetal, the stronger the acid it forms. 

Disproportionation— An oxidation-reduction reaction in which the same chemical species is oxidized and reduced. 

Like other reactive products, H2 and CL are kept apart to prevent explosive recombination. Note the higher liquid level in the anode compartment. This slight hydrostatic pressure difference minimizes backflow of NaOH, which prevents the disproportionation (self-oxidation-reduction) reactions of CL that occur in the presence of OH , such as... 

Cr(rV) is a very unstable intermediate. According to Beattie and Haight Its reactions, including oxidation, reduction and disproportionation, are too fast to admit to its direct detection". However, KaCrF has been prepared and was shown to be iso-morphous with KaMnF Salts of tetrahedral CrOj" are also known ... 

A disproportionation reaction is an oxidation-reduction reaction in which the same substance is oxidized and reduced. Complete and balance the foUowing disproportionation reactions ... 

Among the most common oxidation-reduction reactions are combination, decomposition, combustion, and displacement reactions. A more involved type is called disproportionation reactions, which will also be discussed in this section. 

These disproportionation reactions may be involved in oxidation-reduction reactions by other reagents. Instead of direct oxidation or reduction, the disproportionation reaction can occur first, followed by direct oxidation or reduction of the appropriate product. 

Often several oxidation states of the same ion can coexist in solution, such as Cu and Cu, Fe " and Fe ", or Cr ", Cr " and CrO ". A disproportionation reaction is defined as an oxidation-reduction reaction between two identical ions, producing simultaneously species with higher and lower valences. 

The disproportionation of actinyl(v) ions MOj is the reverse of the oxidation-reduction reactions + In Table 21.23, the rates and... 

For both the oxidation-reduction and disproportionation reactions, AS becomes more favorable, the lower the charge of the activated complex. For the formation of MOj ions, the values of AS are more positive, the more negative the exponent of the hydrogen dependence (Table 21.22). For the disproportionations, the values of AS are more negative, the more positive the exponent of the hydrogen dependence (Table 21.23). 

In some oxidation-reduction reactions, called disproportionation reactions, the same substance is both oxidized and reduced. An example is the decom-postion of hydrogen peroxide, H2O2, into H2O and O2 ... 

Table 6 presents a summary of the oxidation—reduction characteristics of actinide ions (12—14,17,20). The disproportionation reactions of UO2, Pu , PUO2, and AmO are very compHcated and have been studied extensively. In the case of plutonium, the situation is especially complex four oxidation states of plutonium [(111), (IV), (V), and (VI) ] can exist together ia aqueous solution ia equiUbrium with each other at appreciable concentrations. 

The modes of thermal decomposition of the halates and their complex oxidation-reduction chemistry reflect the interplay of both thermodynamic and kinetic factors. On the one hand, thermodynamically feasible reactions may be sluggish, whilst, on the other, traces of catalyst may radically alter the course of the reaction. In general, for a given cation, thermal stability decreases in the sequence iodate > chlorate > bromate, but the mode and ease of decomposition can be substantially modified. For example, alkali metal chlorates decompose by disproportionation when fused ... 

Strategy First (1) set up the Nemst equation for the reduction half-reaction and calculate red. Then (2) repeat the calculation for the oxidation half-reaction, finding Eox. Finally (3), add rcd + ra if the sum is positive, disproportionation should occur. 

The number of chemical reactions used in CVD is considerable and include thermal decomposition (pyrolysis), reduction, hydrolysis, disproportionation, oxidation, carburization, and nitrida-tion. They can be used either singly or in combination (see Ch. 3 and 4). These reactions can be activated by several methods which are reviewed in Ch. 5. The most important are as follows ... 

Homolytic aromatic substitution often requires high temperatures, high concentrations of initiator, long reaction times and typically occurs in moderate yields.Such reactions are often conducted under reducing conditions with (TMSlsSiH, even though the reactions are not reductions and often finish with oxidative rearomatization. Reaction (68) shows an example where a solution containing silane (2 equiv) and AIBN (2 equiv) is slowly added (8h) in heated pyridine containing 2-bromopyridine (1 equiv) The synthesis of 2,3 -bipyridine 75 presumably occurs via the formation of cyclohexadienyl radicals 74 and its rearomatization by disproportionation with the alkyl radical from AIBN. ... 

KEY TERMS oxidation-reduction disproportionation Hess Law exothermic reaction... 

The reaction was considered as an oxidation-reduction process, where the phosphite and TeCl4 are converted into phosphorochloridate and tellurium dichloride, respectively. TeCl2 suffers a disproportionation into Te and TeCl4 which can participate again in the reaction. 

The reactions of nitric oxide involve either oxidation or reduction (or both simultaneously in disproportionation and decomposition). Except for oxidation, these reactions of nitric oxide require catalysts for them to proceed at significant rates. An important stimulus to studying these catalyzed reactions lies in the environmental hazards posed by oxides of nitrogen, of which NO is the parent member, as discussed at the beginning of this section. Particular attention in the area of metal complex catalyzed reactions has focused in the last five years on the reduction of nitric oxide by carbon monoxide, (113). 

For elements of several possible oxidation states (e.g., sulfur, the transition metals) all relevant disproportionation equilibria need to be examined. Pseudo-equilibrium conditions may be maintained for some time, where competing oxidation-reduction systems can be involved. For example, the following kinds of reactions... 

Studies of oxygen isotope fractionation were undertaken to address the mechanisms of the oxidative and reductive phases of SOD catalysis.44 Experiments were conducted at pH 10 in either borate or carbonate buffer where the rate is only slightly diminished from that at physiological pH. Control experiments demonstrated that all of the 02 produced came from the enzymatic reaction rather than the spontaneous disproportionation that occurs in the presence of trace metal ions slowly as the pH is increased. The reaction proceeds rapidly to 100% completion giving equal concentrations of 02 and H202 therefore, a ratio of fractionation factors was determined from the distribution of the lsO isotope in the two products. The ratio of fractionation factors reflects the ratio of KIEs on the oxidative and reductive reactions, and is designated as (3 (Equation 9.9). The (3 was determined to be 1.0104 0.0012 under the conditions described above. 

High temperature thermodynamic data are available only for three sulfites calcium, potassium, and sodium. Most sulfites are fairly unstable, decomposing at relatively low temperatures. The decomposition reactions are not always exactly known, with diverse decomposition products, including sulfur, being reported. There are two major decomposition reactions (1) decomposition to the oxide and S02, and (2) oxidation-reduction (disproportionation) to the sulfate and oxide and S02, i.e.,... 

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