Equilibrium constants for ammonia

In applying these equations, the authors assumed that the adsorption of nitrogen on the iron catalyst in the presence of an ammonia-hydrogen mixture is the same as it would be when at a nitrogen pressure equivalent to the existing partial pressure of ammonia and hydrogen in the gas mixture. Thus, since the equilibrium constant for ammonia synthesis is... 

Although the standard equilibrium constant for ammonia synthesis reaction at 298 K is 6.8 x 10 , the reaction rate is not detectable. To increase the reaction rate and activate catalyst at optimal temperature, the industrial synthesis ammonia is carried out at 400°C-500°C. Because of the thermodynamic limitation, the standard equilibrium constant is 1 x 10 at this temperature which leads to low conversion. In order to enhance conversion, it is common to introduce high pressure and increase concentration of N2 to move the equilibrium to right. However, the conversion of ammonia s3mthesis in one attempt is 10%-15% only. 

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

The equilibrium constant for the decomposition at a certain temperature is 25. Calculate the partial pressures of all the gases at equilibrium if ammonia with a pressure of 1.00 atm is sealed in a 3.0-L flask. 

The equilibrium constant for the solubility reaction is readily calculated. Consider, for example, the reaction by which zinc hydroxide dissolves in ammonia. Again, imagine that the reaction occurs in two steps ... 

Write the equilibrium constant for the ammonia synthesis reaction, reaction C. 

Self-Test 9.7A The equilibrium constant for the ammonia synthesis (reaction C) is K = 41 at 127°C. What is the value of Kc at that temperature ... 

We can also write an equilibrium constant for the proton transfer equilibrium of a base in water. For aqueous ammonia, for instance,... 

Here cnh, is the concentration of undissociated ammonia in water. The equilibrium constant for this class of equilibria is often defined in terms of a Henry s Law constant, Xh-... 

For a reaction at equilibrium, the rate of the forward reaction is balanced exactly by the rate of the reverse reaction. For this reason, any equilibrium reaction can be written in either direction. The equilibrium constant for the Flaber synthesis of ammonia, for example, can be expressed in two ways ... 

Ammonia is an example of a weak base. A weak base generates hydroxide ions by accepting protons from water but reaches equilibrium when only a fraction of its molecules have done so. The equilibrium constant for this type... 

Salts that contain cations of weak bases are acidic. For example, the ammonium cation Is the conjugate acid of ammonia. When ammonium salts dissolve in water, NH4 ions transfer protons to H2 O molecules, generating H3 O and making the solution slightly acidic NH4" ((2 q) + H2 0(/) NH3(c2 q) + H3 O (a q) The equilibrium constant for this reaction can be calculated from Equation and for ammonia (Example ) ... 

Of course, the equilibrium constant Km the latter equation does not have the same value as the ATin the equilibrium equation for ammonia. The numerical value of ATdepends on the particular reaction, the temperature, and the units used to describe concentration. For liquid solutions, the concentrations are usually expressed as molarity. For a mixture of gases, the concentration of each molecular species is commonly given either as molarity or as pressure in atmospheres. 

Figure 3 Fractional surface coverage 0. determined using Eq. (3), as a function of ammonia pressure for (a) an etched w-CdSe crystal and (b) a n-CdSe crystal coated with an ammonia-imprinted PAA film. The insets show the same data as double reciprocal plots, yielding equilibrium constants for (a) and (b) of 750 250 and 1000 500...

An estimate of a lower limit for the equilibrium constant for the formation of adducts from diazines and NH2 (K) has been obtained from the rate of hydrogen exchange of ammonia and from the NMR data. 9 The K value is found to be no smaller than 10s M. Pyrimidines bearing such groups as R2N or phenyl at position 2 display the same behavior as the parent compound and undergo attachment at position 4. The corresponding adducts have been characterized by C-NMR.90... 

The equilibrium constant for the reaction of ammonia with water has the following values in the range 5°-10°C ... 

By contrast, a change in temperature nearly always changes the value of the equilibrium constant. For the Haber synthesis of ammonia, which is an exothermic reaction, the equilibrium constant Kc decreases by a factor of 1011 over the temperature range 300-1000 K (Figure 13.12). 

The stability of a complex ion is measured by its formation constant Kf (or stability constant), the equilibrium constant for formation of the complex ion from the hydrated metal cation. The large value of Kf for Ag(NH3)2+ means that this complex ion is quite stable, and nearly all the Ag+ ion in an aqueous ammonia solution is therefore present in the form of Ag(NH3)2+ (see Worked Example 16.12). 

When dissolved in a solvent, some solutes combine with the solvent to form solvated species. The two outstanding examples in aqueous solution are carbon dioxide to form COz(aq) (carbonic acid) and ammonia to form NH3(aq) (ammonium hydroxide). In many cases the equilibrium constant for the reaction is unknown or not known with sufficient accuracy for thermodynamic purposes. Conventions have been established for treating such systems thermodynamically. Here we discuss the carbon dioxide-water... 

Ketones and aldehydes also condense with other ammonia derivatives, such as hydroxyl amine and substituted hydrazines, to give imine derivatives. The equilibrium constants for these reactions are usually more favorable than for reactions with simple amines. Hydroxylamine reacts with ketones and aldehydes to form oximes hydrazine and its derivatives react to form hydrazones and semicarbazide reacts to form semicarbazones. The mechanisms of these reactions are similar to the mechanism of imine formation. 

Although a statistical factor contributes to the equilibrium constants for many types of reactions, it is in reactions of the type being considered here—the replacement of one neutral ligand by another neutral ligand— that this factor may be the principal factor in causing variation of Kn with n. Other series of reactions of this type are the formation of ammonia complexes in aqueous solution. The variation of Kn with n observed for the chromium (III)/water-methyl alcohol system is slightly smaller than observed for ammonia complexes of cobalt(II) (18) and nickel(II) (19) ... 

More recently, Stedman and coworkers have examined the kinetics of the nitrosation of hydrazine (Perrott et al., 1976), some methyl hydrazines (Perrott et al., 1977) and aryl hydrazines (Stedman and Uysal, 1977). Again (8) is obeyed with S = RNHNH3, and rate constants are believed to represent an encounter-controlled process. Since it is not possible to calculate the true rate constants for processes such as (9) because the equilibrium constant for HjNO formation is not known, arguments are based on the relative constancy of k-values (eqn 8) over a wide range of very reactive species. The products from the reaction of hydrazine itself are ammonia and hydrazoic acid in ratios which vary with the acidity. Both are thought to arise from a common intermediate as laid out in Scheme 4. With excess HNOj, hydrazoic... 

The tremendous thermodynamic driving force of six basic ammonia molecules combining with six protons results in an equilibrium constant for the reaction (Eq. 13.24) c( 10. Neverthdess. addihcation of a solution of hexaamminecobaltdll) results in no immediate change, and several days are required (at room temperature) fm d ra-dation of the comi x despite the favondde thomodynamics. The inertness of the Comdex results from the d)sence of a suitable low-energy pathway for the acidolysis reaction. 

An acid may, rather arbitrarily, be called a strong acid in glacial acetic acid if HAjp - 1- Thus perchloric acid is a strong acid, and yet the pAT for the overall dissociation constant is only 4.87 because it exists largely as ion pairs. Hydrochloric acid has an overall pAT value of 8.55 ammonia, 6.40 pyridine, 6.10 sodium acetate, 6.68 potassium chloride, 6.88 and sodium perchlorate, 5.48. Perchloric acid is the strongest acid and the one used for titration of bases that may be too weak to be titrated in water as solvent. At first it appears that an attempt to titrate a base such as pyridine with perchloric acid would fail, since both have small overall dissociation constants. Critical to the success of such titrations is the small dissociation constant of the salt formed, which results in a large favorable equilibrium constant for the reaction. 

Example 2.5. Dissolution of Ammonia in Water From enthalpy and entropy data (Latimer, 1952), compute the equilibrium constant for the solution of... 

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