Dinitrogen tetroxide-nitrogen dioxide equilibrium

The brown nitrogen dioxide gas eondenses to a yellow liquid whieh freezes to eolourless erystals of dinitrogen tetroxide. Below 150°Cthe gas eonsists of moleeules of dinitrogen tetroxide and nitrogen dioxide in equilibrium and the proportion of dinitrogen tetroxide inereases as the temperature falls. Above 150°C nitrogen dioxide dissoeiates into nitrie oxide and oxygen. 

Nitrogen dioxide forms an equilibrium with dinitrogen tetroxide. When it is cold, the equilibrium favours the second compound. Depending on the thermal conditions, the dangerous reactions will involve one or the other of these two compounds. Their endothermic character makes them hardly stable. 

Figure 7.7 shows how the law of chemical equilibrium applies to one chemical system. Chemists have studied this system extensively. It involves the reversible reaction between two gases dinitrogen tetroxide, which is colourless, and nitrogen dioxide, which is dark brown. 

These are not student tests. Your teacher may demonstrate this equilibrium if a suitable fume hood is available for the first test, and if sealed tubes containing a mixture of nitrogen dioxide, N02(g), and dinitrogen tetroxide, N204(g), are available for the second test. If either or both tests are not demonstrated, refer to the photographs that show the changes. 

The second example demonstrates another aspect of equilibrium by using the transformations between dinitrogen tetroxide and nitrogen dioxide. 

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. 

Sometimes a chemical reaction begins, continues for a while, and then appears to stop before any one of the reactants is used up the reaction is said to have reached equilibrium. The reaction between nitrogen dioxide, NOo, and dinitrogen tetroxide, NgO, provides an interesting example. The gas that is obtained by heating concentrated... 

The quantity K is called the equilibrium constant of the reaction of dissociation of dinitrogen tetroxide to nitrogen dioxide. The equilibrium constant is independent of the pressure of the system, or of the concentration of the reacting substances. It is, however, a function of the temperature. 

Relation to the Principle of Le Chatelier. It can be seen that the equilibrium equation for the reaction corresponds to the principle of Le Chatelier. Let us consider an equilibrium state of the gas such that there are present nitrogen dioxide and dinitrogen tetroxide mole-... 

In some cases it has been found possible to determine the rates of the opposing reactions, and to show experimentally that the ratio of the two rate constants is indeed equal to the equilibrium constant. This has not been done for the nitrogen dioxide-dinitrogen tetroxide equilibrium, however, because the individual chemical reactions take place so rapidly that expetimenters have not been able to determine their rates. It has, indeed, been found by experiment that if the pressure... 

The great rate at which a chemical reaction may occur has been mentioned above in the discussion of the NOg-NgO equilibrium. It was pointed out that the decomposition of dinitrogen tetroxide or reformation of these molecules from nitrogen dioxide molecules occurs within... 

Heat of Reaction and the Tendency of the Reaction to Take Place. It has been pointed out in earlier paragraphs tiiat some reactions tliat take place are exothermic, and some are endothermic. A reacti()n that reaches a measurable equilibrium may be caused to go in either direction, by starting with one set of reactants or another. For example, the reaction involving tiie red gas nitrogen dioxide and the colorless gas dinitrogen tetroxide has a heat effect shown by the following equation ... 

The effect of temperature on the gas-phase equilibrium of nitrogen dioxide, NO2, and dinitrogen tetroxide, N2O4, can be seen because of the difference in color of NO2 and N2O4. The intense brown NO2 gas is the pollution that is responsible for the colored haze that you sometimes see on smoggy days. 

To understand how the nitrogen dioxide-dinitrogen tetroxide equilibrium is affected by temperature, we need to review endothermic and exothermic reactions. Recall that endothermic reactions absorb energy and have positive Mi values. Exothermic reactions release energy and have negative Mi values. The forward reaction is an exothermic process, as the equation below shows. 

The nitrogen dioxide product participates in a rapid equilibrium to dinitrogen tetroxide (Eq. 11.39). 

A mixture of nitrogen dioxide and dinitrogen tetroxide are allowed to come to equilibrium at 30 °C, and their partial pressures are found to be 1.69 atm N2O4 and 0.60 atm NO2. 

The study of physical equilibrium yields useful information, such as the equilibrium vapor pressure (see Section 11.8). However, chemists are particularly interested in chemical equilibrium processes, such as the reversible reaction involving nitrogen dioxide (NO2) and dinitrogen tetroxide (N2O4) (Figure 14.1). The progress of the reaction... 

Nitrogen Dioxide and Dinitrogen Tetroxide. These two oxides, N02 and N204, exist in a strongly temperature-dependent equilibrium... 

The conversion between dinitrogen tetroxide (N2O4) and nitrogen dioxide (NO 2) responds to changes in temperature in an observable way. This endothermic equilibrium is described by the following equation. 

Dinitrogen tetroxide (N2O4), which is in equilibrium with nitrogen dioxide. 

For the first case above, this means that raising the temperature shifts the equilibrium of an endotropic reaction in the direction of increased In the case of an exotropic reaction, this happens in the opposite direction. We have seen this before. But let us have again a look at an example, an equilibrium mixture between brown nitrogen dioxide and colorless dinitrogen tetroxide (Experiment 9.3) (see also Sect. 9.1) ... 

We can illustrate how the law of mass action was discovered empirically and demonstrate that the equilibrium constant is independent of starting concentrations by examining a series of experiments involving dinitrogen tetroxide and nitrogen dioxide ... 

Absorber performance is controlled by temperature and pressure. At reduced temperatures the gas-phase equilibrium moves toward the formation of dinitrogen tetroxide and an increased solubility in HNO3. Therefore, lower temperatures improve the absorption rate and increase the acid concentration. At higher pressures the NO oxidation reaction is quicker, and equilibrium moves toward nitrogen dioxide. In addition, with higher pressure more concentrated nitric acid is produced. 

The equilibrium between dinitrogen tetroxide (colorless) and nitrogen dioxide (brown color) gases favor the formation of the latter as temperature increases (from bottom to top). The models show dinitrogen tetroxide and nitrogen dioxide molecules. 

P12.6 The dissociative gas and important rocket propellant dinitrogen tetroxide is in rapid equilibrium with nitrogen dioxide following the reaction ... 

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