Gas-aqueous reaction

Schwartz, S. E. Gas-Aqueous Reactions of Sulfur and Nitrogen Oxides in Liquid Water Clouds, in S02, NO, and N02 Oxidation Mechanisms. Atmospheric Considerations (J. G. Calvert, Ed.), pp. 173-208 and references therein, Acid Precipitation Series, Vol. 3 (J. I. Teasley, Series Ed.), Butterworth, Stoneham, MA, 1984a. 

Figure 2. Schematic illustration of the subprocesses comprising a gas-aqueous reaction in a single cloud droplet. A represents aqueous phase reagent species transferred from the gas phase B, species in rapid equilibrium with A and C, product species, at the surface of the drop (a) or in the interior (r) PA represents gas-phase partial pressure of A at the surface of the drop (a) and at large distance from the drop (oo).

Schwartz, S. E. (1984) "Gas-Aqueous Reactions of Sulfur and Nitrogen Oxides in Liquid-Water Clouds," Acid Precipitation edited by J. G. Calvert, Butterworth PublTsliers, Boston, MA. 

S. E. Schwartz, Gas-aqueous reactions of sulfur and nitrogen oxides in liquid-water... 

S. E. Schwartz, Gas-aqueous reactions of sulfur and nitrogen oxides in liquid-water clouds, in SO2, NO, and NO2 Oxidation Mechanisms Atmospheric Considerations 0. G. Calvert ed.), Butterworth, Woburn, MA, 1984, p. 173. 

Again with platinized Ti02, ultraviolet irradiation can lead to oxidation of aqueous CN [323] and to the water-gas shift reaction, CO + H2O = H2 + CO2 [324]. Some mechanistic aspects of the photooxidation of water (to O2) at the Ti02-aqueous interface are discussed by Bocarsly et al. [325]. 

The gas phase reaction shows a double minimum and a small barrier along the reaction coordinate which is the difference between the two C-CL distances. The minima disappear in aqueous solution and this is accompanied by an increase in the height of the barrier. The behaviour in dimethyl fonnamide is intennediate between these two. 

Increasing or decreasing the partial pressure of a gas is the same as increasing or decreasing its concentration. The effect on a reaction s equilibrium position can be analyzed as described in the preceding example for aqueous solutes. Since the concentration of a gas depends on its partial pressure, and not on the total pressure of the system, adding or removing an inert gas has no effect on the equilibrium position of a gas-phase reaction. 

Alkanolamines in aqueous soludon react widi carbon dioxide and hydrogen sulfide to yield salts, important to gas condidoiiing reactions. Tlie dissociation of die salts upon heating results in recovery of the original starting material. Tliese reactions fomi the basis of an important industrial apphcadon, ie, die "sweetening" of natural gas. 

Hypochlorous acid and chlorine monoxide coexist in the vapor phase (78—81). Vapor pressure measurements of aqueous HOCl solutions show that HOCl is the main chlorine species in the vapor phase over <1% solutions (82), whereas at higher concentrations, CI2O becomes dominant (83). The equihbtium constant at 25°C for the gas-phase reaction, determined by ir and uv spectrophotometry and mass spectrometry, is ca 0.08 (9,66,67,69). The forward reaction is much slower than the reverse reaction. 

Dehydrochlorination of chlorinated derivatives such as 1,1,2-trichloroethane may be carried out with a variety of catalytic materials, including Lewis acids such as aluminum chloride. Refluxing 1,1,2-trichlorethane with aqueous calcium hydroxide or sodium hydroxide produces 1,1-dichloroethylene in good yields (22), although other bases such as magnesium hydroxide have been reported (23). Dehydrochlorination of the 1,1,1-trichloroethane isomer with catalytic amounts of a Lewis acid also yields 1,1-dichloroethylene. Other methods to dehydrochlorinate 1,1,1-trichloroethane include thermal dehydrochlorination (24) and by gas-phase reaction over an alumina catalyst or siUca catalyst (25). 

This is the so-called water-gas shift reaction (—AG29gl9.9kJmoP ) and it can also be effected by low-temperature homogeneous catalysts in aqueous acid solutions. The extent of subsequent purification of the hydrogen depends on the use to which it will be put. 

In general, a multitude of different phenomena of flow, heat and mass transfer occur during a liquid/liquid or gas/liquid reaction. Rather than discussing all relevant effects, which would be a tremendous task, the focus of this section is solely on flow phenomena in either single-phase aqueous systems or air/water systems. 

In cyclohexane the same two ketones (12) and (13) are obtained from the photolysis of (11) but in aqueous dioxane two phenols are isolated as well as the bicyclic ketone (12). Swenton(10) suggested that the gas-phase reaction involves diradical species, whereas in polar solvents zwitterionic intermediates are favored ... 

Gas phase reactions are not so common in producing solid oxides and will not be considered here. As far as liquid state reactions are concerned, these can be performed in aqueous and non-aqueous solvents and can be subdivided into (i) precipitation and co-precipitation, including the so-called template synthesis, (ii) evaporation, and (iii) sol-gel methods. 

Solutions prepared from Ru3(C0)i2in acidic aqueous diglyme solutions are shown to be catalysts for the water gas shift reaction under reasonably mild conditions (100°C, Pco=l atm). 

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