Equilibrium-hydrogen

Figure 7.12 Dependence of the hydrogen equilibrium pressure on the unit-cell volume of various LnNij-type compounds (Ln = rare earth). Open circles, LnCoj closed circles, LnNij open triangles, LaCo, (Following Buschow van...

For hydrogen equilibrium pressures below 100 Torr, an absorption technique was used. Thoroughly activated samples were outgassed at 500° C to a vacuum... 

Nickel sulfide coatings are therodynamically unstable at the hydrogen equilibrium potential. NiS2 decomposes simply by immersion in aqueous KOH. In aqueous alkaline solution at hydrogen-evolving cathodes, all NiS, phases are reduced according to... 

For isotopes other than those of hydrogen, equilibrium isotope effects are usually small (ca. <3%), and such isotopes are more often used in labelling studies with their concentrations at a particular position reflecting the probability of a mechanistic pathway, without consideration of the effects of isotopic substitution upon stability of isotopomers. Positional exchange in recovered reactants, for example, provides supporting evidence of intermediates and their nature, and Scheme 9.15 illustrates one dissociative process and one associative process. 

The R(Ni,Fe,Al)5 hydrogen storage alloy prepared on the base of the commercial cerium ligature (R = Ce, La, Pr, Nd), lanthanum and nickel (both of technical purity grade) has been used in the unit. The composition of the alloy must provide a hydrogen equilibrium pressure of 10 bar over MH at room temperature and above 150 bar at elevated temperatures. 

In the entire absence of hydrogen, equilibrium is reached very slowly,... 

Fig. 8. Comparison of the IINS spectra (TOSCA, ISIS) of palladium catalysts (a) IINS spectrum of the spent catalyst as taken directly from the hydrogenation process and sealed under argon, (b) same sample as in (a) after solvent extraction, (c) same sample as in (a) and (b) after hydrogenation at hydrogen equilibrium partial pressures up to 1.5 bar, and (d) a used but still active catalyst as characterized after cleaning by solvent extraction under the same conditions as the deactivated sample. The spectra are normalized to the same total sample mass.

At a given temperature T, this reaction has a hydrogen equilibrium pressure H. Consider now a solid solution of this metal with a non-hydride forming metal (B). The relative partial molar free energy of A in the alloy is AGa- If the resulting alloy AB reacts with hydrogen as... 

H/Pd atomic ratio (n) for a-phase equals 0.008, and the minimal n for P-phasc equals 0.607. The interval between these n values corresponds to the biphase field in which the increasing in n does not cause an increase in the hydrogen equilibrium pressure. With an increasing temperature, hydrogen solubility in palladium decreases and the biphase field cuts down. The mutual transformations of the two phases create strains in the material and may result in a splitting of the membrane. 

In the dehydrogenation of ethane, CO and H2O were produced under CO2. Thus, one possible reason for the promoting effects is to shift the dehydrogenation-hydrogenation equilibrium by removing H2 from the products. However, this contribution does not seem to be significant, since ethane conversion is below equilibrium at the temperature examined. As mentioned above, the removal or suppression of carbon deposition seems to... 

Badger, R. M., The ammonia, carbon, hydrogen cyanide, hydrogen equilibrium and the free energy of hydrogen cyanide, J. Am. Chem. Soc., 46, (1924), 2166-2172. Cited on page 433. 

Iodine-Hydrogen Equilibrium. This example should elucidate, using model drawings, that equilibrium sets in from both directions (see Fig. 6.8). It does not matter if one assumes an equimolar mix of iodine vapor and hydrogen gas, or one of pure hydrogen iodide gas in both cases, one reaches an identical... 

Moreover, Takehara (125) has investigated the hydrogenation of allyl alcohol. Since the rate was found to depend on the rotational speed of the platinum disk only to a minor extent, the reaction was not diffusion controlled. The potential of the platinum disk was about 50 to 120 mV more noble than the hydrogen equilibrium potential. The potential... 

Additionally, in order to accurately calculate F values from exchange data we need to account for the salt effect on the oxygen and hydrogen equilibrium isotope fractionation between minerals and fluids, based on results reported by Horita et al. (1993a,b 1995) and Chacko et al. (this volume). These results indicate the mineral - salt fractionation may be 0.6 to 1 per mil smaller than the mineral-pure water fractionation at 300°C for a 5 m NaCl solution (Horita et al. 1995). This type of data will play an important role in the ultimate accuracy of the rate constants calculated from partial exchange experiments involving minerals and salt solutions. 

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