Nitrogen dioxide dimerization equilibrium

Nitrogen dioxide dimerizes almost instantly to an equilibrium mixture with nitrogen tetroxide ... 

The nitric oxide which is formed reacts with oxygen to form nitrogen dioxide. Nitrogen dioxide exists in equilibrium with its dimer, dinitrogen tetroxide. The nitrogen dioxide/dimer mixture is sent to a column, sometimes called an absorption tower. Water is added at the top of the column. The nitrogen dioxide is converted to nitric acid. Byproduct nitric oxide is oxidized to nitrogen dioxide by means of a stream of air passed into the absorption column. The aqueous nitric acid is removed continuously from the base of the column. Overall, the reaction can be written as ... 

Nitrogen dioxide, N02 (oxidation number -t-4), is a choking, poisonous, brown gas that contributes to the color and odor of smog. The molecule has an odd number of electrons, and in the gas phase it exists in equilibrium with its colorless dimer N204. Only the dimer exists in the solid, and so the brown gas condenses to a colorless solid. When it dissolves in water, NOz disproportionates into nitric acid (oxidation number +5) and nitrogen oxide (oxidation number +2) ... 

The organic substrates in Chart 8 can be divided into two main categories in which (i) the oxidation of olefins, sulfides, and selenides involves oxygen atom transfer to yield epoxides, sulfoxides, and selenoxides, respectively, whereas (ii) the oxidation of hydroquinones and quinone dioximes formally involves loss of two electrons and two protons to yield quinones and dinitrosobenzenes, respectively. In order to provide a unifying mechanistic theme for the seemingly disparate transformations in Chart 8, we note that nitrogen dioxide exists in equilibrium with its dimeric forms, namely, the predominant N—N bonded dimer 02N—N02 and the minor N—O bonded isomer ONO—N02 (equation 88). 

Nitrogen dioxide is a stable radical with an unpaired electron and forms the dimer N204 in the equilibrium reaction ... 

Nitrogen dioxide readily converts to other forms of nitrogen oxides. It coexists in equilibrium with its dimeric form, N2O4. The latter is more stable at ordinary temperatures. 

Nitrogen dioxide rapidly forms an equilibrium mixture with its dimer, dinitrogen tetroxide or nitrogen peroxide [see Eq. (9.11)]. The formation of the tetroxide is favored by low temperature and high pressure104. 

Nitrogen dioxide, NOg, a red gas, and its dimer dinitrogen tetrox-ide, N0O4, a colorless, easily condensable gas, exist in equilibrium with one another ... 

This effect is illustrated by the equilibrium between nitrogen dioxide (NO2) and its dimer, dinitrogen tetraoxide (N2O4) (briefly considered in Example 9.6) expressed by the chemical equation... 

Nitrogen dioxide (N02) dimerizes almost instantaneously to an equilibrium mixture of N02 and N204 as shown in Reaction 3.13. This reaction is also favored at lower temperatures and increasing pressures. 

The determination of nitric oxide by gas chromatography is complicated by the equilibrium existing between nitric oxide and nitrogen dioxide in the presence of air or oxygen, and by the dimerization of the dioxide. 

The first coefficient describes the most common case, namely how much entropy AS flows in if the temperature outside and (also inside as a result of entropy flowing in) is raised by AT and the pressure p and extent of the reaction are kept constant. In the case of the secmid coefficient, volume is maintained instead of pressure (this only works well if there is a gas in the system). In the case of J = 0, the third coefficient characterizes the increase of entropy during equilibrium, for example when heating nitrogen dioxide (NO2) (see also Experiment 9.3) or acetic acid vapor (CH3COOH) (both are gases where a portion of the molecules are dimers). Multiplied by T, the coefficients represent heat capacities (the isobaric Cp at constant pressure, the isochoric Cy at constant volume, etc.). It is customary to relate the coefficients to the size of the system, possibly the mass or the amount of substance. The corresponding values are then presented in tables. In the case above, they would be tabulated as specific (mass related) or molar (related to amount of substance) heat capacities. The qualifier isobaric and the index p will... 

As mentioned, nitrogen dioxide is a radical. It s a reddish-brown gas under ordinary conditions and exists in equilibrium with the dimer N2O4, a colorless diamagnetic species ... 

The mixture is a pungent brownish liquid that boils at 2UC. Lower temperatures and increasing pressure shift the reaction to the production of nitrogen tetroxide. Nitrogen dioxide is a brown paramagnetic species while the dimer is colorless and diamagnetic at 21°C the equilibrium mixture contains 0.08% NOg. 

This chapter is devoted to a consideration of the results obtained in studies of the interactions of nitrogen oxides with polymers. There are eight nitrogen oxides, but only NO, NO2 and N-,04 are actually important as pollutants. Nitric oxide (NO) exists as a free radical, but it is reasonably stable in reactions with organic compounds. The paramagnetic nitrogen dioxide (NO2) is more active compared with NO. This gas is universally present in equilibrium with its dimer molecule ... 

With one unpaired electron, nitrogen dioxide is ripe for the dimerization represented in Equation (16.38). This equilibrium is highly temperature-dependent. 

Nitrogen monoxide and nitrogen dioxide are both reactive free radicals (they contain unpaired electrons). At low temperature, two NO2 molecules dimerize to form N2O4, pairing their two lone electrons. If N2O4 is heated it decomposes back to NO2. Consequently, the equilibrium between NO2 and N2O4 is highly temperature-dependent, as we saw in Section 14.9. 

---