Equilibrium H2 concentration

Hydrogen sulfide can fracture into hydrogen and sulfur merely by thermal decomposition, but the equilibrium H2 concentrations are at best those shown in Table I. 

In this study, the experiment based on a combination of two reactions illustrated in Table II was carried out. The equilibrium H2 concentration generally becomes higher with a decrease in temperature in the sulfurization of the metal sulfides by H2S, while... 

The sulfur composition of FeS ranges from FeS +o t0 Fe l+0.2 at 600°C, and the equilibrium H2 concentration in that range varies from about 100 % to about 4 %. On the other hand, the composition of the thermally decomposed product was FeS n under normal pressure and FeSp 06 under reduced pressure. The sulfurized products were both approximately FeS 2 Therefore, the H2 formation behavior in the figure was explained as showing a concentration corresponding closely to the composition-variation of FeS. 

Ni3S2 is a known lower sulfide as compared to NiS and shows a high equilibrium H2 concentration over a wide range of sulfur compositions. ... 

Generally, the sulfurization of metal exhibits a remarkably high equilibrium H2 concentration, compared to the sulfurization of metal sulfide as shown in Table III. 

However, few sulfides are capable of being thermally decomposed into metal and sulfur. Noting the decomposibility of Soliman et al(l) proposed a cycle using Bi. The authors found tnat Ag2S decomposed at 800°C, under a reduced pressure of a few mm Hg, to form Ag. The equilibrium H2 concentrations for sulfurizations are, however, small for both Bi and Ag. The reaction is hindered by the sulfide film formed on the surface which occurs during the sulfurization of solid metal. 

The equilibrium H2 concentration was 99.8 % at 500°C and 97.9 % at 800°C. The value is very high, in spite of the temperature being high. As a result, the higher the reaction temperature, the more favorable the H2 formation behavior in this reaction system. In addition, the sulfurization of Pb is an exothermic reaction and a slight rise in temperature was observed during the experiment. However, the acceleration of the reaction at low temperature was also examined. 

The calculated equilibrium H2S concentration at a temperature range from 0 to 900 °C in ZnO-ZnS H20-H2S system in the presence of different concentration of H20(g) are shown in Figure 5.18.183 It is clear that the low temperature is favor for decreasing the equilibrium H2S concentration, as the reaction is exothermic. The presence of H20(g) has a significant effect on the equilibrium H2S concentration. At 600 °C, when H20(g) concentration increases from 0.1 to 20 vol %, the corresponding equilibrium H2S concentration increases significantly from 3.7 x 10 3ppbv to... 

Figure 5.18. The calculated equilibrium H2S concentration at a temperature range from 0 to 900 °C for ZnO + H2S o ZnS + H20 reaction in the presence of different concentrations of H2Q(g)-...

The product of this reaction is partly water vapour and partly another chemically active free radical (H). The interaction of processes [3.2] and [3.3] results in an equilibrium H2 concentration. 

If alunite, K-mica and kaolinite (which are common minerals in the advanced argillic alteration) are in equilibrium, the concentration of H2SO4 can be estimated based on the experimental work by Hemley et al. (1969) the concentration of H2SO4 at 200°C and 300°C is 0.002 and 0.012 M, respectively. This may suggest that it is difficult to form such a high concentration of sulfate ion only by oxidation of H2S. 

A practical difficulty should be mentioned here, which is also relevant to all processes that require exchange of H2 between the gas and solution phases. Methods (2) and (3) depend on measuring the partial pressure of hydrogen in the gas phase over the solution. They depend on the assumption that the gas phase is in equilibrium with the solution, and this is not necessarily the case, unless there is vigorous mixing. The rate of exchange of gas molecules is surprisingly slow, particularly at low H2 concentrations. 

Water gas shift and steam reforming reactions producing H2 under rich conditions (reactions R6 and R7 in Table III, respectively) start to be significantly active at the temperatures above 300 °C (cf. Fig. 22c. These reactions result in a different actual CO C3H6 H2 concentration ratio inside the monolith in comparison with the raw exhaust gas, or the synthetic rich inlet gas mixture used in the lab experiments (Koci et al., 2007b). The reactions with water are characterized by the evaluated rate constants kj T) as well as by the thermodynamic equilibrium constants Keq(7). 

At the lowest temperature where the para-H2 and ortho-H2 concentrations are in thermal equilibrium, the rotational ground state and the lowest excited state (J = 0 and 1) are about equally populated, hence the comparable line intensities at 354 and 587 cm-1 at 77 K. With increasing temperature, the J = 1 state is more highly populated, and states with J > 1 are increasingly populated as well, at the expense of the J = 0 ground state, so that the So(l) line shows up much more prominently than So(0) at the higher temperatures. Profiles obtained at temperatures T > 100 K may similarly be fitted by simple three-parameter model profiles if one accounts for the higher So(J) and Qo(J) lines, J > 1, as well. Very satisfactory fits of the laboratory data have resulted [15]. The profiles of the individual lines vary with temperature. Fairly accurate empirical spectra may be constructed, even at temperatures for which no measurements exist, when the empirical temperature dependences of the three BC parameters are known, see Chapter 5 below. 

Fig. 3.12. The rototranslational absorption spectrum of H2-He pairs at three temperatures 77.4 K ( ), 195 K (x), and 293 K ( ). The data shown represent the enhancement of the absorption due to the addition of helium to hydrogen gas, obtained in 32 mole percent equilibrium hydrogen concentration in helium by subtraction of the H2-H2 spectra after [37].

The equilibrium amount of nitric oxide (0.12%) demands for its formation the entire available amount of oxygen (0.6%). However, in reality the formation of 0.12% NO merely causes a decrease in H20 from 24.2% to 24.1% and an increase in H2 from 4.3% to 4.4% the equilibrium oxygen concentration changes by less than 5% of its magnitude. 

Suppose that we have an equilibrium mixture of 0.50 M N2,3.00 M H2, and 1.98 M NH3 at 700 K, and that we disturb the equilibrium by increasing the N2 concentration to 1.50 M. Le Chatelier s principle tells us that reaction will occur to relieve the stress of the increased concentration of N2 by converting some of the N2 to NH3. As the N2 concentration decreases, the H2 concentration must also decrease and the NH3 concentration must increase in accord with the stoichiometry of the balanced equation. These changes are illustrated in Figure 13.8. 

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