Hydrogen-nitrogen-ammonia equilibrium

When a technical language is adopted by those who do not share the expertise of its parent community, it may actually become distorted, and this may make it even more difficult for students to keep clear what different forms of symbolism mean. So in biology lessons students are likely to meet equations representing photosynthesis and aerobic respiration (Examples 7 and 8 in Table 4.1). When just considering the substances involved, these two equations will seem to stand in the same relation as those discussed for the hydrogen/nitrogen-ammonia equilibrium ... 

Essential for synthesis considerations is the abiUty to determine the amount of ammonia present ia an equiUbrium mixture at various temperatures and pressures. ReHable data on equiUbrium mixtures for pressures ranging from 1,000 to 101,000 kPa (10 —1000 atm) were developed early on (6—8) and resulted ia the determination of the reaction equiUbrium constant (9). Experimental data iadicates that is dependent not only on temperature and pressure, but also upon the ratio of hydrogen and nitrogen present. Table 3 fists values for the ammonia equilibrium concentration calculated for a feed usiag a 3 1 hydrogen to nitrogen ratio and either 0 or 10% iaerts (10). 

Calculate the equilibrium partial pressure of hydrogen if the equilibrium partial pressures of ammonia and nitrogen are 0.015 atm and 1.2 atm, respectively. 

Consider the statement The equilibrium constant for a mixture of hydrogen, nitrogen, and ammonia is 3.41. What information is missing from this statement ... 

FIGURE 9.10 These graphs show the changes in composition that can be expected when additional hydrogen and then ammonia are added to an equilibrium mixture of nitrogen, hydrogen, and ammonia. Note that the addition of hydrogen results in the formation of ammonia, whereas the addition of ammonia results in the decomposition of some of the added ammonia as reactants are formed. In each case, the mixture settles into a composition in accord with the equilibrium constant of the reaction. 

Pressure affects the gases in a system much more than it affects the liquid or solids. We will investigate the same ammonia, hydrogen, nitrogen system discussed above. If the system is at equilibrium, what will an increase in pressure by the chemist do to the equilibrium The system will shift to try to reduce the stress, as required by Le Chatelier s principle. How can this system reduce its own pressure By reducing the total number of moles present. It can shift to the right to produce 2 mol of gas for every 4 mol used up ... 

Hydrogen gas is added to an equilibrium system of hydrogen, nitrogen, and ammonia. The equilibrium shifts to reduce the stress of the added hydrogen. How much hydrogen will be present at the new equilibrium compared with the old equilibrium—more, less, or the same concentration ... 

A mixture of nitrogen, hydrogen and ammonia gases are in a sealed container and are at equilibrium. Which of the following changes will affect the reaction quotient (gc) but not affect the equilibrium constant (K )7... 

FIGURE 9.2 In an experiment showing that equilibrium is dynamic, a reaction mixture in which N2 (pairs of blue spheres), D2 (pairs of yellow spheres), and ND3 have reached equilibrium is mixed with one with the same concentrations of N2, H2 (pairs of white spheres), and NH3. After some time, the concentrations of nitrogen, hydrogen, and ammonia are found to be the same, but the D atoms are distributed among the hydrogen and ammonia molecules. 

Self-Test 9.15B Nitrogen, hydrogen, and ammonia gases have reached equilibrium in a 1.00-L container at 298 K. Equilibrium partial pressures are 0.080 atm N2, 0.050 atm H2, and 2.60 atm NH3. 

PI5.1 Show that in reaction (15.1), assuming ideal behavior of the gases, the maximum (equilibrium) conversion of nitrogen and hydrogen into ammonia at a given temperature and total pressure, is obtained when the reacting gases are in the proportion of 1 to 3. (To do so, suppose that the N2 and H2 molecules are present in the ratio of 1 to r, with x as the mole fraction of NH3 present at equilibrium. Then express Kp in terms of mole fractions and the total pressure, and find the condition that makes dx/dr equal to zero.)... 

This equation can be illustrated easily with reference to the equilibrium between nitrogen, hydrogen and ammonia in the gaseous phase ... 

For this equilibrium, the equilibrium constant, Kx, (see Appendix and Frames 43 section 43.3), which is, in this example, conveniently written in terms of the mole fractions xn2, xh2 and xnh3 of nitrogen, hydrogen and ammonia present, is given by ... 

EXAMPLE 16.3. Suppose that, under a certain set of conditions, a mixture of nitrogen, hydrogen, and ammonia is at equilibrium. The concentration of hydrogen is 0.0350 moEL that of nitrogen is 0.0100 moEL, and that of ammonia is 0.0250 mo EL. Now 0.0003 mol of hydrogen is added to 1.00 L of the mixture. What is the widest possible range of hydrogen concentration in the new equilibrium ... 

When gaseous nitrogen, hydrogen, and ammonia are mixed in a closed vessel at 25°C, no apparent change in the concentrations occurs over time, regardless of the original amounts of the gases. It would seem that equilibrium has been attained. However, this is not necessarily true. 

The second reason applies to the nitrogen, hydrogen, and ammonia mixture at 25°C. Because the molecules involved have strong chemical bonds, mixtures of N2, H2, and NH3 at 25°C can exist with no apparent change over long periods of time. However, under appropriate conditions the system does reach equilibrium, as shown in Fig. 6.5. Note that because of the reaction stoichiometry, H2 disappears three times as fast as N2 does, and NH3 forms twice as fast as N2 disappears. 

Suppose we have a mixture of gaseous nitrogen, hydrogen, and ammonia at equilibrium (Fig. 6.8). If we suddenly reduce the volume, what will happen to the equilibrium position The reaction system can reduce its volume by reducing the number of molecules present. Consequently, the reaction... 

As the reaction proceeds, the rate of the forward reaction continues to decrease and the rate of the reverse reaction continues to increase until the two rates are equal. At that point, ammonia is being produced as fast as it is being decomposed, so the concentrations of nitrogen, hydrogen, and ammonia remain constant, as shown in Figures 18-2c and 18-2d. The system has reached a state of balance or equilibrium. The word equilibrium means that opposing processes are in balance. Chemical equilibrium is a state in which the forward and reverse reactions balance each other because they take place at equal rates. 

Find the molar flow rates of all species out of an equilibrium reactor when the inlet values of nitrogen, hydrogen, and ammonia are 1.1,3, and 0.2, The equilibrium constant is 0.05 at 589 K... 

The next modification you will try allows phase equilibrium in the separator where most of the ammonia is condensed. For simplicity, though, you should set the conversion per pass in the reactor to 25 percent Change the separator so that it is a phase separation. The A -values are nitrogen, 4.8 hydrogen, 70 ammonia, 0.051 carbon dioxide, 0.32. (Remember that the symbol K value is used in both chemical reaction equilbria and phase equilibria, but K represents different things in those two cases.) The flow rates of nitrogen and hydrogen into the process are 1 and 3 mol per time unit, respectively, but there is also 0.01 mol per time unit of carbon dioxide. Because of the carbon dioxide,... 

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