Ammonia equilibrium with elements

Ammonia Equilibrium. In school experiments, it is possible to quantitatively decompose ammonia gas with the help of a nickel catalyst into its components. From 50 ml ammonia, we can get 100 ml gas, namely 25 ml nitrogen and 75 ml hydrogen (see E6.7). However, it is not possible to reverse the procedure under normal pressure, i.e. to achieve the ammonia synthesis from the elements. The volume-temperature diagram (see Fig. 6.10) confirms this one does not get any noticeable traces of ammonia at a pressure of 1 bar. In contrast, ammonia can almost be completely produced from the deployed gases at 200°C and a pressure of 1000 bar ... 

It was already generally accepted that molecular nitrogen was too inert to react directly with hydrogen at moderate temperatures. Unfortunately, at high temperatures where reaction with hydrogen becomes possible, the decomposition of ammonia also takes place, hence the need for a catalyst to allow synthesis at the reaction temperature. Perman used iron as a catalyst in 1904 and studied the formation of ammonia from its elements, but, unfortunately for him, in the presence of moisture which we now know retards the reaction. Haber immediately realized that the equilibrium concentration of ammonia should not be infiuenced by the presence of moisture. 

Cinnamic acid (48) is synthesized universally in higher plants and widely in fungi from (25)-phenylalanine by phenylalanine ammonium lyase. This process is a trans elimination of the elements of ammonia, with stereospecific loss of the 3-pro S) proton of phenylalanine (46). Phenylpyruvic acid (49) (shown in its enol form) is the normal biogenetic precursor of phenylalanine, and is in equilibrium with it by means of the action of aminotransferases and amino acid oxidases (see Fig. 11). To distinguish between the participation of cinnamic acid (48) and phenylpyruvic acid (49) and to clarify the mechanism involved in the proton losses, (2R,35)-[3- H]-, (2S,3R)-[3- H], and (25)-[f/- C]phenylalanines were administered to the cultures. The incorporations resulted in the removal of 57% and 76%, respectively, of the labeled hydrogen. 

The formation of alkali-metal and alkaline-earth-metal sulphides and polysulphides from the elements in liquid ammonia has been extensively studied in the past, but the reactions between the metals and hydrogen sulphide in liquid ammonia have drawn detailed attention only recently. It has been suggested that the equilibrium of H2S in this solvent to give the solvated hydrosulphide ion accounts for the formation of KSH even with an excess of metal. With the alkaline-earth metals, effective preparative methods have been developed for the sulphides from H2S in liquid ammonia but anhydrous hydrosulphides have not been obtained. Now, hydrosulphides have been prepared of the form M(SH)2,xNH3 (M = Ca, Sr, or Ba x — 4, 6, or 0, respectively) from the metals with H2S in ammonia, but the compounds are stable only at low temperatures. Those of Ca and Sr are stable at —45 °C but decompose to the monosulphides at room temperature. Ba(HS)2 decomposes to BaS at 100 °C with evolution of a mole of H2S. For M (SH) (M = Rb or Cs), thermal decomposition gives polysulphides. The hydrosulphides of Rb, Cs, Sr, and Ba hydrolyse rapidly in moist air.74... 

Commercially it is obtained by catalytic oxidation of ammonia as already noted. Direct combination of the elements occurs only at very high temperatures, and to isolate the small amounts so formed (a few volume per cent at 3000°) the equilibrium mixture must be rapidly chilled. Though much studied, this reaction has not been developed into a practical commercial synthesis. Nitric oxide reacts instantly with 02 ... 

A 20.0-L vessel is filled with 1.00 mol of ammonia, NH3. What percent of ammonia dissociates to the elements if equilibrium is reached at 345°C Use data from Appendix C and make any reasonable approximation to obtain K. 

All three curves exhibit the same basic shape, with the high-temperature regions merging together for all of the catalysts. The conversion in this regime is determined by the thermodynamic equilibrium between ammonia and its constituent elements. The experimental curve falls along the calculated curve with a... 

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