Thermodynamics of ammonia

Due to the equilibrium ammonia concentration changes with H2/N2 according to thermodynamics of ammonia synthesis reaction. Therefore, outlet ammonia concentration cannot directly reflect the influence of H2/N2 on catal3dic activity. Hence, the catalytic efficiency is defined as the ratio of outlet ammonia concentration to equilibrium ammonia concentration at the same conditions. The effect of H2/N2 on catalytic efficiency for Ba-Ru-K/AC catalyst is shown in Table 6.45. It can be... 

When building up the Institute in Dahlem, Haber made limited use of the advantages offered by the Berlin physical chemistry community. Van t Hoff died the year Haber arrived in Berlin, while Haber and Nemst had previously engaged in a heated dispute concerning the thermodynamics of ammonia synthesis and were not close personally. Moreover, Haber brought most of the initial Institute staff with him from Karlsruhe. 

Ma.nufa.cture. Nickel carbonyl can be prepared by the direct combination of carbon monoxide and metallic nickel (77). The presence of sulfur, the surface area, and the surface activity of the nickel affect the formation of nickel carbonyl (78). The thermodynamics of formation and reaction are documented (79). Two commercial processes are used for large-scale production (80). An atmospheric method, whereby carbon monoxide is passed over nickel sulfide and freshly reduced nickel metal, is used in the United Kingdom to produce pure nickel carbonyl (81). The second method, used in Canada, involves high pressure CO in the formation of iron and nickel carbonyls the two are separated by distillation (81). Very high pressure CO is required for the formation of cobalt carbonyl and a method has been described where the mixed carbonyls are scmbbed with ammonia or an amine and the cobalt is extracted as the ammine carbonyl (82). A discontinued commercial process in the United States involved the reaction of carbon monoxide with nickel sulfate solution. 

Ammonia is readily absorbed ia water to make ammonia liquor. Figure 2 summarizes the vapor—Hquid equiUbria of aqueous ammonia solutions and Figure 3 shows the solution vapor pressures. Additional thermodynamic properties may be found ia the Hterature (1,2). Considerable heat is evolved duriag the solution of ammonia ia water approximately 2180 kJ (520 kcal) of heat is evolved upon the dissolution of 1 kg of ammonia gas. 

Nitric acid is one of the three major acids of the modem chemical industiy and has been known as a corrosive solvent for metals since alchemical times in the thirteenth centuiy. " " It is now invariably made by the catalytic oxidation of ammonia under conditions which promote the formation of NO rather than the thermodynamically more favoured products N2 or N2O (p. 423). The NO is then further oxidized to NO2 and the gases absorbed in water to yield a concentrated aqueous solution of the acid. The vast scale of production requires the optimization of all the reaction conditions and present-day operations are based on the intricate interaction of fundamental thermodynamics, modem catalyst technology, advanced reactor design, and chemical engineering aspects of process control (see Panel). Production in the USA alone now exceeds 7 million tonnes annually, of which the greater part is used to produce nitrates for fertilizers, explosives and other purposes (see Panel). 

It was clearly shown by NMR spectroscopy that the addition of ammonia or primary or secondary alkylamines at position 5 of the 1,2,4-triazine 4-oxides to give the adducts 89 is a kinetically controlled process, while addition at position 3 to form the ring-opening products 85 is a thermodynamically controlled process. 

Erom thermodynamic properties of ammonia greater than a datum of -40°E ... 

The production of ammonia is of historical interest because it represents the first important application of thermodynamics to an industrial process. Considering the synthesis reaction of ammonia from its elements, the calculated reaction heat (AH) and free energy change (AG) at room temperature are approximately -46 and -16.5 KJ/mol, respectively. Although the calculated equilibrium constant = 3.6 X 108 at room temperature is substantially high, no reaction occurs under these conditions, and the rate is practically zero. The ammonia synthesis reaction could be represented as follows ... 

These effects are shown in Figure 17.4, where the entropy of ammonia, NH3> is plotted versus temperature. Note that the entropy of solid ammonia at 0 K is zero. This reflects the fact that molecules are completely ordered in the solid state at this temperature there is no randomness whatsoever. More generally, the third law of thermodynamics tells us that a completely ordered pure crystalline solid has an entropy of zero at 0 K. 

Examples and underscore a dilemma faced by industrial chemists and engineers. Example shows that at 298 K the equilibrium position of the Haber reaction strongly favors the formation of ammonia. Why then is the Haber s Tithesis not carried out at 298 K The reason is that even with a catalyst, the reaction is much too slow to be useful at this temperature. Thermodynamics favors the product, but the kinetics of the reaction are unfavorable. 

For example, classic thermodynamic methods predict that the maximum equUi-brium yield of ammonia from nitrogen and hydrogen is obtained at low temperatures. Yet, under these optimum thermodynamic conditions, the rate of reaction is so slow that the process is not practical for industrial use. Thus, a smaller equilibrium yield at high temperature must be accepted to obtain a suitable reaction rate. However, although the thermodynamic calculations provide no assurance that an equUibrium yield will be obtained in a finite time, it was as a result of such calculations for the synthesis of ammonia that an intensive search was made for a catalyst that would allow equilibrium to be reached. 

The thermodynamic equilibrium constant K for the formation of ammonia according to the equation... 

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