Temperatures saturation activity

A 50.0-liier tank contains an air-carbon tetrachloride mixture at 1 atm absolute, 34°C, and 30.0% relative saturation. Activated carbon is placed in the tank to adsorb CCI4. The temperature of the tank contents is maintained at 34°C, and clean air is continuously supplied to the lank throughout the process to maintain the total pressure at 1.00 atm. The process may be shown schematically as follows ... 

Air-saturated water has a dissolved O2 concentration dependent on temperature, the Henry s law constant and ionic strength. In pure water at 0 °C, O2 saturation is 450 p,M at 25 °C, saturation falls to 270 p,M. Other solutes reduce O2 solubility, such that at normal seawater salinities, O2 saturation is reduced by —25%. Seawater is, of course, rarely at perfect O2 saturation. Active photosynthesis may locally increase O2 production rates, resulting in supersaturation of O2 and degassing to the atmosphere. Alternately, aerobic respiration below the sea surface can consume dissolved O2 and lead to severe 02-depletion or even anoxia. 

Surface plane Adsorbate Adsorbed species Initial sticking coefficient Saturation coverage, lO sites cm LEED pattern at 25 C FD peak temperatures, °C Activation energies for desorption of original adsorbate, kJ mole Ref... 

The stability relationships between calcite, dolomite and magnesite depend on the temperature and activity ratio of Mg " /Ca " (Fig. 5d). Lower Mg/Ca activity ratios are required to induce the dolomitization of calcite and to stabilize magnesite at the expense of dolomite (Fig. 5d) (Usdowski, 1994). Formation waters from the Norwegian North Sea reservoirs have an average log(an g -/ cz- ) - TO to 0.0 and thus fall within the stability field of dolomite. Nevertheless, both calcite and dolomite are common cements in these rocks, indicating that dolomitization is a kinetically controlled reaction. Further evidence of this is revealed from Recent sediments, such as the Fraser River delta in Canada (Simpson Hutcheon, 1995) (log (aMg2+/aca=+) -2.2 to h-1.0), where the pore waters are saturated with respect to dolomite, but it is calcite rather than dolomite that precipitates. Calcite rather than dolomite forms below the deep>-sea floor, yet the pore waters plot at shallow, near sea bottom temperatures in the stability field of dolomite and shift with an increase in depth towards the stability field of calcite (Fig. 5d). This shift is due to a diffusion-controlled, downhole decrease in Mg/Ca activity ratio caused by the incorporation of Mg in Mg-silicate that results from the alteration of volcanic material, a process which is coupled with the release of calcium (McDuff Gieskes, 1976). 

Fig. 8. Effect of the water content of the system on the rate of S5mthesis of dodecyl decanoate catalyzed hy the lipase from Rhizomucor miehei (formerly known as Mucor miehei). 0.5 M of each substrate was dissolved in the appropriate solvent (hexane (V), toluene (A), trichloroethylene (o), isopropyl ether ( ), pentane-3-one (0)). In the case of pure reactants (+), an equimolar amount was used (2.4 Af). Water activity is defined as a- = p/po, where p is the vapor pressure of water in the system and po is the vapor pressure of pure water at the same temperature. Water activity was controlled through the vapor phase by equilibration with various saturated salt solutions. Reprinted from Ref (70), cop5Tight 1992, with kind permission from Elsevier Science).

Isopiestic studies involve equilibration of the water in a small sample with that in a large reference mixture of known water activity, via transport through the vapor phase. Because of its poor solubility at room temperature, the activity of water in saturated solutions of C12MG will be very close to 1 therefore, the reference mixture selected was pure water. Elemental analytical data established that the starting sample was dry. Isopiestic... 

Low temperature Saturated fatty acid chains High water activity Low ionic strength Neutral/high pH... 

Many of them seem to represent ancestors who are believed to have been active in the early history of this planet (high temperature, reducing atmosphere). Organisms are usually not restricted to grow at a certain temperature. Adaptation within a range of 20°C-30°C above or below their optimized growth temperature is possible. It is achieved by a modification of the fatty acid composition in the cytoplasmic membrane. At higher temperatures, unsaturated and/or branched fatty acids prevail, whereas, at lower temperatures saturated, unbranched ones are found. 

Reactions with Ammonia and Amines. Acetaldehyde readily adds ammonia to form acetaldehyde—ammonia. Diethyl amine [109-87-7] is obtained when acetaldehyde is added to a saturated aqueous or alcohoHc solution of ammonia and the mixture is heated to 50—75°C in the presence of a nickel catalyst and hydrogen at 1.2 MPa (12 atm). Pyridine [110-86-1] and pyridine derivatives are made from paraldehyde and aqueous ammonia in the presence of a catalyst at elevated temperatures (62) acetaldehyde may also be used but the yields of pyridine are generally lower than when paraldehyde is the starting material. The vapor-phase reaction of formaldehyde, acetaldehyde, and ammonia at 360°C over oxide catalyst was studied a 49% yield of pyridine and picolines was obtained using an activated siHca—alumina catalyst (63). Brown polymers result when acetaldehyde reacts with ammonia or amines at a pH of 6—7 and temperature of 3—25°C (64). Primary amines and acetaldehyde condense to give Schiff bases CH2CH=NR. The Schiff base reverts to the starting materials in the presence of acids. 

Quicklime and hydrated lime are reasonably stable compounds but not nearly as stable as their limestone antecedents. Chemically, quicklime is stable at any temperature, but it is extremely vulnerable to moisture. Even moisture in the air produces a destabilizing effect by air-slaking it into a hydrate. As a result, an active high calcium quicklime is a strong desiccant (qv). Probably hydrate is more stable than quicklime. Certainly hydrated lime is less perishable chemically because water does not alter its chemical composition. However, its strong affinity for carbon dioxide causes recarbonation. Dolomitic quicklime is less sensitive to slaking than high calcium quicklime, and dead-burned forms are completely stable under moisture-saturated conditions. 

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