The Formation of Nitrogen Oxides

The formation of the nitrogen oxides, nitric oxide (NO) and nitrogen dioxide (NO2) from N2 and O2, provides an example of the interplay between thermodynamics and kinetics. The calculation of the equilibrium concentrations of NO and NO2 is straightforward if we assume that these are the only compounds formed and that the initial pressures of N2 and O2 are known. 

The enthalpies and free energies of formation of NO and NO2 are just the values given above, since N2 and O2 are the constituent elements. There are two things to note about these values. First, AG for the formation of NO is more positive than that for NO2 at 298 K. Second, AH for NO formation is much more positive than AH for NO2 formation. Thus, according to the van t Hoff equation, the equilibrium constant for NO formation will increase much more rapidly as the temperature is increased. 

We may describe the temperature dependence of AG and AH in terms of the functions Gj — H29s)/T and Hr — H298- These functions are easily interpolated to obtain values at temperatures intermediate to the points given in the tables. The equilibrium pressures of NO and NO2 are given in Fig. 

The equilibrium pressure for NO2 is much greater than the NO pressure for temperatures less than about 500 K. Above 1000 K, the NO pressure is much greater than the NO2 pressure. The following discussion will focus on NO formation. 

The reason for considering this equilibrium at high temperatures is that there are many processes that 

---

Because of the formation of nitrogen oxides, a steady-state ozone concentration cannot be obtained instead, due to the buHdup of nitrogen oxides, an increase in residence time in the discharge results in a decrease in ozone concentration beyond the maximum value. Thus, there is an optimum residence time for maximum ozone production. 

New low-NO, burners are effective in reducing emissions from both new power plants and existing plants that are being retrofitted. Low NO, burners limit the formation of nitrogen oxides by controlling the mixing of fuel and air, in effect... 

What are the mechanisms in combustion that result in the formation of nitrogen oxides ... 

When nitrogen and oxygen gases were present then it was possible to get fixation of nitrogen with the formation of nitrogen oxides. Molecules of nitrogen and oxygen dissociated in the cavitation bubbles to form initially NO radicals [33, 34]. 

Which of the amino acids contribute to the formation of nitrogen oxides What is the consequence of the presence of this nitrogen to our atmospheric air ... 

In dynamic flash combustion, the tin-encapsulated sample is dropped into the preheated furnace shortly after the flow of a 50 vol% O2/50 vol% He mixture is started (Figure 27-8). The Sn capsule melts at 235°C and is instantly oxidized to Sn02, thereby liberating 594 kJ/mol, and heating the sample to 1 700°-l 800°C. If the sample is dropped in before very much Oz is present, decomposition (cracking) occurs prior to oxidation, which minimizes the formation of nitrogen oxides. (Flammable liquid samples would be admitted prior to any 02 to prevent explosions.)... 

The formation of nitrogen oxides in combustion and explosions has been studied by many scientists, but to date there is no uniform opinion on the question of the nature and mechanism of this process. Nernst [1] believed that in an explosion, as a result of the high temperature, a direct bimolec-ular reaction of molecular oxygen with molecular nitrogen occurs. Haber... 

Recently, work on nitrogen oxidation in the combustion of a fuel mixed with air has become extensive in connection with pollution of the environment by toxic combustion products (including NO). An good review of this research was done by A. N. Heiherst and I. M. Vincent,7 and by A. Macek for coal combustion.8 Detailed experimental and theoretical work on the formation of nitrogen oxides in turbulent gas flames was performed by P. Moreau and R. Borghi.9... 

It must always be assumed that explosive fumes and propellant fumes are to some extent toxic. Excess oxygen causes the formation of nitrogen oxides, deficiency carbon monoxide, both toxic. In the United States, the following classification of toxic fume components has been accepted a 1 -1/4 by 8" cartridge in its cartridge paper is detonated in a -> Bichel Bomb, and the fume composition is gas analysed. In the following Table toxic gases means the sum CO + H2S (NO and N02 are not considered ) in ft3/lb explosive ... 

Cold, concentrated nitric acid renders iron passive in this state it does not react with dilute nitric acid nor does it displace copper from an aqueous solution of a copper salt. 1 +1 Nitric acid, or hot, concentrated nitric acid dissolves iron with the formation of nitrogen oxide gas and iron(III) ions ... 

The dissolution in nitric acid is accompanied with the formation of nitrogen oxide ... 

Dolan, E. Zhang, Y. Klarup, D. The Distribution Coefficient of Atrazine with Illinois Soils ALaboratory Exercise in Environmental Chemistry, /. Chem. Educ. 1998, 75, 1609-1610. Driscoll, J. A. Acid Rain Demonstration The Formation of Nitrogen Oxides as By-Products of High Temperature Flame in Connection with Internal Combustion Engines, /. Chem. Educ. 1997, 74, 1424-1425. 

Subsequently, the obtained photolysis rate constants were adjusted for Arctic summer conditions as observed on the Greenland ice sheet. Further calculations with the adjusted rate constants demonstrated that under natural conditions the formation of nitrogen oxides... 

When waste materials contain nitrogen bound in organic molecules, they can contribute to the formation of nitrogen oxides. The primary mechanism of NO t formation in this case is the conversion of fuel-bound nitrogen to HCN and HNCO, followed by the conversion of these species into NH and then to NO, as described above. NO2 and N2O can also form in combustion processes through reactions such as ... 

During flame combustion, temperatures in excess of 1700K occur. At those temperatures, the reaction between the air constituents nitrogen and oxygen is thermodynamically favored, resulting in the formation of nitrogen oxides, according to the overall reaction equation... 

---