Partial-pressure format

Accordingly, the gas-phase partial-pressure format could be used by substituting... 

The value has been extrapolated because, at temperatures above 170°C, the rate of reaction 2 rapidly iucreases and it is difficult to determine the carbamate vapor pressure owiag to the formation of water and urea and the consequent lowering of the partial pressure of ammonium carbamate. 

The reaction mechanism and rates of methyl acetate carbonylation are not fully understood. In the nickel-cataly2ed reaction, rate constants for formation of methyl acetate from methanol, formation of dimethyl ether, and carbonylation of dimethyl ether have been reported, as well as their sensitivity to partial pressure of the reactants (32). For the rhodium chloride [10049-07-7] cataly2ed reaction, methyl acetate carbonylation is considered to go through formation of ethyUdene diacetate (33) ... 

Because of the relative instabiUty of FeO, the reduction to metallic Fe occurs at a much lower temperature and appreciable CO2 is present in the product gas. The high temperature required for the reaction of MnO and C results in the formation of essentially pure CO the partial pressures of CO2 and Mn are <0.1 kPa (1 X 10 atm). The product of this reaction is manganese carbide (7 3) [12076-37-8J, Mn C, containing 8.56% carbon. Assuming immiscibility of the metal and carbide, Mn should be obtainable by the reaction of MnO and Mn C at 1607°C. However, at this temperature and activity of Mn, the partial pressure of Mn vapor is approximately 10 kPa (0.1 atm) which would lead to large manganese losses. 

Low temperatures strongly favor the formation of nitrogen dioxide. Below 150°C equiUbrium is almost totally in favor of NO2 formation. This is a slow reaction, but the rate constant for NO2 formation rapidly increases with reductions in temperature. Process temperatures are typically low enough to neglect the reverse reaction and determine changes in NO partial pressure by the rate expression (40—42) (eq. 13). The rate of reaction, and therefore the... 

Reactions involving collisions between two molecular species such as H2 and I2, or between two HI molecules are called bimolecular or second-order homogeneous reactions, because they involve the collision between two molecular species, and they are homogeneous since they occur in a single gas phase. The rates of these reactions are dependent on the product of the partial pressure of each reactant, as discussed above, and for the formation of HI, and the decomposition of HI,... 

When one of the elements is solid, as in tire case of carbon in the calculation of the partial pressures of tire gaseous species in the reaction between methane and air, CO(g) can be used as a basic element together widr hydrogen and oxygen molecules, and thus the calculation of the final partial pressure of methane must be evaluated using the equilibrium constant for CH4 formation... 

Adsorbed molecules are more strongly held at the sites where the weakest metal-metal bonding is to be found, and these conespond to the active sites of Langmuir. A demonstration of this effect was found in smdies of the adsorption of H2S from a H2S/H2 mixture on a single crystal of copper of which die separate crystal faces had been polished and exposed to die gas. The formation of copper sulphide first occuiTed on die [100] and [110] planes at a lower H2S partial pressure dran on die more densely packed [111] face. Thus die metal atoms which are less strongly bonded to odrer metal atoms can bond more strongly to die adsorbed species from die gas phase. 

In the steam reforming reaction, /rC02/p C0 = 2.08 (hr = 5.64) at this temperamre, and at lOOOK the results are hr A = 0.55 for carbon formation, and the PCO2/p CO ratio is 0.155 (hr A = 1.16), and tlrus the tendency for carbon formation passes from zero to unity in tlris temperature range. The presence of CO2 is not indicated in this reaction as given above, but its partial pressure can be obtained from data for the concunent reaction... 

FORMAT (IX, INPUT THE EXIT PARTIAL PRESSURES OF HYDROGEN,, CARBON MONOXIDE, /3X, AND METHANOL IN ATMOSPHERES,IN, THAT ORDER )... 

To fully understand the formation of the N13S2 scale under certain gas conditions, a brief description needs to be given on the chemical aspects of the protective (chromium oxide) Ci 203/(nickel oxide) NiO scales that form at elevated temperatures. Under ideal oxidizing conditions, the alloy Waspaloy preferentially forms a protective oxide layer of NiO and Ci 203 The partial pressure of oxygen is such that these scales are thermodynamically stable and a condition of equilibrium is observed between the oxidizing atmosphere and the scale. Even if the scale surface is damaged or removed, the oxidizing condition of the atmosphere would preferentially reform the oxide scales. 

A higher steam/hydrocarhon ratio favors olefin formation. Steam reduces the partial pressure of the hydrocarbon mixture and increases the yield of olefins. Heavier hydrocarbon feeds require more steam than gaseous feeds to additionally reduce coke deposition in the furnace tubes. Liquid feeds such as gas oils and petroleum residues have complex polynuclear aromatic compounds, which are coke precursors. Steam to hydrocarbon weight ratios range between 0.2-1 for ethane and approximately 1-1.2 for liquid feeds. 

The presence of non-condensable gases in steam systems (e.g. air and CO2) will reduce the partial pressure of the steam, and hence its temperature, thus affecting the output of the appliance. A further adverse effect is the presence of a non-condensable gas at the inside surface of a heat emitter. These impede condensation and, hence, heat output. It is therefore imperative that suitable means are provided to prevent formation of CO2 and to evacuate all gases from the system. 

Consider Ni exposed to Oj/HjO vapour mixtures. Possible oxidation products are NiO and Ni (OH)2, but the large molar volume of Ni (OH)2, (24 cm compared with that of Ni, 6.6 cm ) means that the hydroxide is not likely to form as a continuous film. From thermodynamic data, Ni (OH)2 is the stable species in pure water vapour, and in all Oj/HjO vapour mixtures in which O2 is present in measurable quantities, and certainly if the partial pressure of O2 is greater than the dissociation pressure of NiO. But the actual reaction product is determined by kinetics, not by thermodynamics, and because the mechanism of hydroxide formation is more complex than oxide formation, Ni (OH)2 is only expected to form in the later stages of the oxidation at the NiO/gas interface. As it does so, cation vacancies are formed in the oxide according to... 

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