Equilibrium partial pressure ratio

According to De Maria and co-workers (1972), the dicarbide is always the most abundant gaseous molecular species in the equilibrium vapor over the corresponding rare-earth-carbide-graphite system, followed by the tetracarbide. Table 8 shows examples of equilibrium partial-pressure ratios, P(RC2)/P(R) and P(RC4)/P(R), at the specified temperatures. 

Reaction quotient (Q) An expression with the same form as Kbut involving arbitrary rather than equilibrium partial pressures, 333-334 Reaction rate The ratio of the change in concentration of a species divided by the time interval over which the change occurs, 285 catalysis for, 305-307 collision model, 298-300 concentration and, 287-292,314q constant, 288 enzymes, 306-307 egression, 288... 

If only the spins of the nuclei are altered in a given transition, the translational and vibrational contributions to the partition function are identical. Thus, for tiie reaction ortho-Hz - para-H2, the partial-pressure ratio at equilibrium is given by... 

The partial pressure ratio, Pcq2PH2 /PH2cPco> is decreased by the absorption of carbon dioxide. Thus, the equilibrium of the reaction 3.12 may be kept at a higher temperature simultaneously with the C02 absorption. The expression of the overall reaction is written as follows ... 

In recent studies, pesticides such as atrazine have been found in precipitation. Therefore volatilization and subsequent transport in the gaseous phase is an important environmental pathway. Vaporization rates of pesticides deposited on surface of soil and plant leaves depend on the physical-chemical properties of the substance. A useful physicochemical criterion is Henry s constant, Ku, which is defined as the equilibrium air-to-water partial pressure ratio of the substance (see Chapter 7). 

Based on the standard Gibbs free energy of the various oxides, three triple points can be calculated WO2.72. WO2.9, WO2 at about 600°C, W02,9, WO3, WO2 at about 270°C, and WO2, WO2.72, W at 1480°C. Using this data, a phase diagram can be constructed. The stability of the various oxides is shown in Fig. 8.2 with respect to the partial pressures of H2O and H2, and temperature. Because aU of these compositions are equilibrium compositions, any of them can be produced simply by annealing W or WO3 at the given partial pressure ratio and temperature. 

Contradictory data on the kinetics of ammonia synthesis, especially in the earlier literature, in some circumstances may reflect a lack of attention to the influence of impurities in the gas. If oxygen compounds are present in the synthesis gas, reversible poisoning of the adsorbing areas, in accordance with an equilibrium depending on the temperature and the water vapor-hydrogen partial pressure ratio, must be taken into account when developing rate equations (see also Section 3.6.1.5). 

Fig. 2 Existence of pure and mixed iron oxides as a function of the partial pressure ratios H2O/H2 and C02/CO, respectively. The equilibrium con iosition of the producer gas after conversion is indicated with PI (pure iron oxide) and P2 (manganese iron...

FIG. 200. The conditions for the formation of magnetite Fc304 (Smiltens, 1952). The numbers on the curves specify the equilibrium partial pressure of oxygen in MPa at various CO CO2 ratios. 

Supersaturation is defined as the ratio of the product of the gas-phase partial pressures in the real state to the product of the corresponding equilibrium partial pressures and is expressed by [12]... 

One mechanism for the removal of Ca is the precipitation of calcite, already noted as one of the principal cementing minerals, in the bedrock. The fact that groundwaters in the drift and bedrock aquifers are generally oversaturated with respect to calcite (see Fig. 5) supports the existence of this mechanism. The saturation indices indicate that calcite either precipitates from solution or simply does not dissolve. Fig. 17 is a plot of the log of the activity ratio of [Ca ] /[Mg ] vs. log of the equilibrium partial pressure of CO2, using computations made with SOLMNEQ. Apparently, the [Ca ]/ [Mg ] ratio of groundwater from the drift aquifers is controlled by calcite and dolomite in as much as similar concentrations of Ca and Mg are in solution. In the bedrock aquifers, precipitation of CaCO3 likely accounts for the decrease in the [Ca ] /[Mg ] ratio and the drop in partial pressure of CO2. ... 

From consideration of the thermodynamics of sulfur chemisorption on ruthenium (ref. 6), the gas phase sulfur activities (llgS/l ) of the lightly and moderately sulfur-poisoned Ru catalysts in equilibrium with the adsorbed sulfur at the process temperature (190 C), were approximately 0.02 and 1 ppb+ respectively. On the basis of these results, the equivalent partial pressure ratio for critical sulfur coverage is about 1 ppb at 490 C. This level is well below that attainable by conventional sulfur removal methods. Thus our result confirms the need for high performance desulfurization technology (ref 3) that can reduce sulfur contaminants in feedstocks to a sufficiently low sulfur level to avoid carbon fouling cf Ru/A Og steam reforming catalysts. 

The partial pressure ratio p(H2S)/p(H2) of the gas phase in equilibrium with the high-temperature modification of Ni3S2 was determined as a function of composition at... 

A mixture of metallic nickel and nickel oxide (particle size around 1 pm) was treated with mixtures of water vapour and hydrogen gas at temperatures ranging from 711 to 860 K, The ratio of equilibrium partial pressures was determined by a ten-... 

We find that the Kelvin equation for the critical cluster size depends on the ratio of the product of the partial pressures of NH3 and HCl to the equilibrium constant Kp. The product pNH,f>HCi must exceed Kp for a critical cluster to exist. Physically this condition merely means that the product of the gas-phase partial pressures must exceed the equilibrium partial pressure product at that temperature for a solid phase to exist. It is equivalent to the condition that 5 > 1 for a critical cluster to exist for homogeneous-homomolecular nucleation. 

Solution Since the reaction started with oidy pure NO2, the equilibrium concentration of NO must be twice the equihbrium concentration of O2, due to the 2 1 mole ratio of the balanced equation. Therefore, the equilibrium partial pressure of NO is (2 x 0.25 atm) = 0.50 atm. 

H2O and the experimental values of the partial pressure ratio(PcH4PH2o) /(Pco P H2) plotted against temperature. Since the experimental ratios are well above the equilibrium constant, introducing a methanation catalyst would decrease the methane yield and thereby increase the heat required to carry out the gasification reaction. 

Depending on the partial pressure ratio F hj/ HjS nickel can be poisoned due to its reaction with sulfur or regenerated (when the ratio is higher than the equilibrium value) [45]. 

The equilibrium conditions for each reaction may be expressed in terms of the partial pressure ratios of CO to CO2 and are illustrated in Eigure 5.1. As a simplification this assumes solid-gas reactions with unit activity of the solid oxide reactants. If in the molten phase, such as PbO dissolved in slag, the activity will be much lower and the eqnihbrinm ratios for COiCOj will be correspondingly higher. For partial pressure ratios of one or above, covering the bulk of the reactions zones of the shaft. Figure 5.1 indicates that PbO reduction should proceed readily, ZnO can be reduced to zinc vapour above 800°C, and iron oxides will be reduced primarily to FeO. In Figure 5.1 the ZnO reduction equilibrium is shown for a zinc vapour partial pressure of 0.01 atmospheres or one per cent in the gas stream. Zinc partial pressure will vary widely however, this serves only to illustrate that zinc vapour will be present at partial pressures of this order. 

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