Ammonia stoichiometry

Unfortunately, in most cases not all the available information on a reaction is given in the reaction equation in a publication, and even less so in reaction databases. To obtain a fuller picture of the reaction that was performed, the text describing the experimental procedure in the publication or a lab journal) would have to be consulted. Reaction products that are considered as trivial, such as water, alcohol, ammonia, nitrogen, etc., are generally not included in the reaction equation or mentioned in the text describing the experimental work. This poses serious problems for the automatic identification of the reaction center. It is highly desirable to have the full stoichiometry of a reaction specified in the equation. 

Iron(III) ammonium citrate [1185-57-5] is of indefinite stoichiometry. A brown hydrated compound [1332-98-5] of iron(III) ammonium citrate contains 16.5—18.5% iron, - 9% ammonia, and 65% citric acid. A green hydrated compound [1333-00-2] contains 14.5—16% iron, 1% ammonia, and 75% citric acid. Iron ammonium citrates are water soluble but are insoluble in alcohol. The compounds are used to fortify bread, milk, and other foods (see... 

The amount of combustion ait is tightly controlled to maximize sulfur recovery, ie, maintaining the appropriate reaction stoichiometry of 2 1 hydrogen sulfide to sulfur dioxide throughout downstream reactors. Typically, sulfur recoveries of up to 97% can be achieved (7). The recovery is heavily dependent on the concentration of hydrogen sulfide and contaminants, especially ammonia and heavy hydrocarbons, ia the feed to the Claus unit. 

Some nitrate is also formed, thus the HOCl/NH stoichiometry is greater than theoretical, ie, - 1.7. This reaction, commonly called breakpoint chlorination, involves intermediate formation of unstable dichloramine and has been modeled kinetically (28). Hypobromous acid also oxidizes ammonia via the breakpoint reaction (29). The reaction is virtually quantitative in the presence of excess HOBr. In the case of chlorine, Htde or no decomposition of NH occurs until essentially complete conversion to monochloramine. In contrast, oxidation of NH commences immediately with HOBr because equihbrium concentrations of NH2Br and NHBr2 are formed initially. As a result, the typical hump in the breakpoint curve is much lower than in the case of chlorine. 

The mauve colored cobalt(II) carbonate [7542-09-8] of commerce is a basic material of indeterminate stoichiometry, (CoCO ) ( (0 )2) H20, that contains 45—47% cobalt. It is prepared by adding a hot solution of cobalt salts to a hot sodium carbonate or sodium bicarbonate solution. Precipitation from cold solutions gives a light blue unstable product. Dissolution of cobalt metal in ammonium carbonate solution followed by thermal decomposition of the solution gives a relatively dense carbonate. Basic cobalt carbonate is virtually insoluble in water, but dissolves in acids and ammonia solutions. It is used in the preparation of pigments and as a starting material in the preparation of cobalt compounds. 

The respiratory quotient (RQ) is often used to estimate metabolic stoichiometry. Using quasi-steady-state and by definition of RQ, develop a system of two linear equations with two unknowns by solving a matrix under the following conditions the coefficient of the matrix with yeast growth (y = 4.14), ammonia (yN = 0) and glucose (ys = 4.0), where the evolution of C02 and biosynthesis are very small (o- = 0.095). Calculate the stoichiometric coefficient for RQ =1.0 for the above biological processes ... 

The stoichiometry of decomposition of [Ni(NH3)4](NCS)2 was dependent on the method of salt preparation [1126]. Ammonia was lost in three successive steps (—NH3, —NH3, —2 NH3) from the solution-prepared salt, but the first intermediate could not be isolated from the similar reaction of material prepared by heterogenous reaction. The difference in behaviour was ascribed to differences in perfection of the crystallites resulting from the alternative preparative methods. 

The synthesis of 4-unsubstituted DHPs in a focused microwave reactor has been reported using alkyl acetoacetates and hexamethylenetetramine 19 as the source of both formaldehyde and ammonia, with additional ammonium acetate to maintain the stoichiometry [57], Irradiation for 100 s under solvent-free conditions gave, for example, 1,4-DHP 20 in 63% isolated yield (Scheme 5). 

Part (d) of the question in Fig. 8.8 required students to draw a microscopic representation of the contents of the container after the reaction. Just over a quarter of the cohort were able to draw a correct representation of the reaction mixture, namely ammonia and the agent in excess. Almost a fifth of students drew a suitable sub-micro representation of the product molecules but did not include the reagent in excess. About one third of the responses contained a wide variety of incorrect submicro representations. Even though students had been taught stoichiometry using sub-micro diagrams such as Fig. 8.4, a number of them (19%) drew diagrams con-... 

A table of amounts is a convenient way to organize the data and summarize the calculations of a stoichiometry problem. Such a table helps to identify the limiting reactant, shows how much product will form during the reaction, and indicates how much of the excess reactant will be left over. A table of amounts has the balanced chemical equation at the top. The table has one column for each substance involved in the reaction and three rows listing amounts. The first row lists the starting amounts for all the substances. The second row shows the changes that occur during the reaction, and the last row lists the amounts present at the end of the reaction. Here is a table of amounts for the ammonia example ... 

The balanced equation shows that three molecules of oxygen are consumed for every two molecules of propene and two molecules of ammonia. Thus, the rate of C3 Hg and NH3 consumption is only two-thirds the rate of O2 consumption. Those seven molecules of starting materials produce two molecules of CH2 CHCN and six molecules of H2 O. Thus, CH2 CHCN is produced at the same rate as C3 Hg is consumed, whereas H2 O is produced three times as fast as CH2 CHCN is. The link between relative reaction rates and reaction stoichiometry is Equation. Therefore,... 

Formylthiophene thiosemicarbazone, 26, as well as the N-methylfhio-semicarbazone, and N-phenylthiosemicarbazone, each yield complexes of stoichiometry [Ni(26-H)2] from heated aqueous alcohol solutions brought to above pH = 7 with ammonia [209]. All complexes are four-coordinate, diamagnetic and the thiophene sulfur does not bond to the nickel(II) center. 

The ammonia necessary for the reaction is the main hindrance to the SCR-NH3 process because pure ammonia is an irritating and toxic gas which cannot be released in the exhaust line. Particular care must be taken to ensure that the maximal NH3 content released in the exhaust does not exceed the threshold of 10 ppm. NH3 release in the exhaust line can be prevented by keeping the overall urea/NOx ratio significantly below stoichiometry or by installing an NH3 clean-up catalyst behind the SCR catalyst. 

However, some contradictory results were obtained in several studies. For instance, in the CH4-NO reaction, some authors have reported that N20 was the primary product [95] while others found that ammonia was first produced [96], The presence of water can play a decisive role since H20 allows generating H2 by WGS or steam reforming [59], Olefins generally show a higher activity than alkanes. Propene for instance has been found more reactive than propane. Some exceptions should be quoted, ethylene has been found less reactive than CH4 in NO reduction at stoichiometry [97],... 

Hinshelwood and Burk [J. Chem. Soc., 127 (1105), 1925] have studied the decomposition of ammonia over a heated platinum filament at 1138° C. The reaction stoichiometry is... 

Widespread medicinal use of colloidal bismuth subcitrate (CBS) has prompted extensive studies of bismuth compounds involving the citrate anion. Bismuth citrate is essentially insoluble in water, but a dramatic increase in solubility with increasing pH has been exploited as a bio-ready source of soluble bismuth, a material referred to as CBS. Formulation of these solutions is complicated by the variability of the bismuth anion stoichiometry, the presence of potassium and/ or ammonium cations, the susceptibility of bismuth to oxygenation to Bi=0, and the incorporation of water in isolated solids. Consequently, a variety of formulas are classified in the literature as CBS. Solids isolated from various, often ill-defined combinations of bismuth citrate, citric acid, potassium hydroxide, or ammonium hydroxide have been assigned formulas on the basis of elemental analysis data or by determination of water and ammonia content, but are of low significance in the absence of complementary data other than thermal analysis (163), infrared spectroscopy (163), or NMR spectroscopy (164). In this context, the Merck index lists the chemical formula of CBS as KgfNHJaBieOafOHMCeHsCbh in the 11th edition (165), but in the most recent edition provides a less precise name, tripotassium dicitrato bismuthate (166). 

A quick look at the reaction suggests that the rate of this ammination reaction should be k[Cu2+(aq)][NH3(aq)]4, where the power of 4 derives from the stoichiometry (provided that the reaction as written was the rate-determining step). It would be a fifth-order reaction, and we would expect that doubling the concentration of ammonia would cause the rate to increase 16-fold (because 24 = 16). But the increase in rate is not 16-fold and, as we have just seen, a fifth-order reaction is not likely. 

Data on the rate of the homogeneous reaction have been obtained by following the decay of ammonia behind shock waves. The stoichiometry of the ammonia decomposition is... 

This balanced equation can be read as 1 nitrogen molecule reacts with 3 hydrogen molecules to produce 2 ammonia molecules. But as indicated previously, the coefficients can stand not only for the number of atoms or molecules (microscopic level), they can also stand for the number of moles of reactants or products. The equation can also be read as 1 mol of nitrogen molecules reacts with 3 mol of hydrogen molecules to produce 2 mol of ammonia molecules. And if the number of moles is known, the number of grams or molecules can be calculated. This is stoichiometry, the calculation of the amount (mass, moles, particles) of one substance in a chemical reaction through the use of another. The coefficients in a balanced chemical equation define the mathematical relationship between the reactants and products, and allow the conversion from moles of one chemical species in the reaction to another. 

As always, we must first discern or find out (from standard tables) the reaction stoichiometry involved. In this case, addition of ammonia to cupric ion effects the well-known reaction, Cu " -I- 2NH3 -> [Cu(NH3)2] +. 

Apart from hydrocarbons and gasoline, other possible fuels include hydrazine, ammonia, and methanol, to mention just a few. Fuel cells powered by direct conversion of liquid methanol have promise as a possible alternative to batteries for portable electronic devices (cf. below). These considerations already indicate that fuel cells are not stand-alone devices, but need many supporting accessories, which consume current produced by the cell and thus lower the overall electrical efficiencies. The schematic of the major components of a so-called fuel cell system is shown in Figure 22. Fuel cell systems require sophisticated control systems to provide accurate metering of the fuel and air and to exhaust the reaction products. Important operational factors include stoichiometry of the reactants, pressure balance across the separator membrane, and freedom from impurities that shorten life (i.e., poison the catalysts). Depending on the application, a power-conditioning unit may be added to convert the direct current from the fuel cell into alternating current. 

The first evidence that post-transition elements, the metals especially, could be reduced to highly colored anions was published over 90 years ago by Joannls (O who discovered that sodium and lead or their alloys dissolve In liquid ammonia to yield an Intensely green-colored solute. A stoichiometry of 2.25 lead atoms per sodium ( ) for what was evidently an anion led Kraus ( ) to formulate this as Pbg ". Until the past decade the principal Information regarding this and many other species were the stoichiometries obtained by Zintl and coworkers from... 

Feuer and co-workers ° conducted extensive studies into alkaline nitration with nitrate esters, exploring the effect of base, time, stoichiometry, concentration, solvent, and temperature on yields and purity. Reactions are generally successful when the substrate a-proton acidity is in the 18-25 p A a range. Alkoxide bases derived from simple primary and secondary aliphatic alcohols are generally not considered compatible in reactions using alkyl nitrates. Optimum conditions for many of these reactions use potassium tert-butoxide and amyl nitrate in THF at —30 °C, although in many cases potassium amide in liquid ammonia at —33 °C works equally well. 

It appears that nitrates can be reduced by H 2 already at very low temperatures (from 60 °C), leading to the formation of ammonia and of minor amounts of N2 (Figure 13.18a). The overall H2 consumption is in line with the stoichiometry of the following reactions leading to the formation of NH3 and N2 ... 

The results ofNH3 TPSR experiment (Figure 13.18b) show that ammonia reduces the stored nitrates starting from 150 °C with formation of nitrogen according to the follovrtng overall stoichiometry ... 

On the basis of these data, the following mechanism for reduction by hydrogen can be suggested. H2, activated over the Pt sites according to the Pt-catalyzed pathway discussed previously, reduces the stored nitrates directly to ammonia or, more likely, induces the decomposition of nitrates to gaseous NO, which are then reduced by H2 to NH3 over the Pt sites [overall reaction (13.47)]. Once ammonia has been formed, it can react with adsorbed nitrates and this reaction is very selective towards nitrogen. It is worth noting that the reaction of ammonia with NOx obeys the stoichiometry of reaction (13.49), which is different from that of the well-known NH3-NO SCR reaction because it implies the participation of nitrates. 

NO (nitrogen monoxide) is the primary NO component in the flue gas meaning that the first equation above is the more significant one. Stoichiometry reveals that one mole of ammonia is required to reduce one mole of NO and convert it to nitrogen and water. Reaction rates are indicative of the Arrhenius equation that describes temperature dependent reactions. 

Hydrogen cyanide is generally produced in industrial quantities by high temperature catalytic reaction between ammonia, methane, and air (the Andrussow process). The stoichiometry of the process is ... 

---