Ammonia reverse reaction

Thermodynamics and Kinetics. Ammonia is synthesized by the reversible reaction of hydrogen and nitrogen. 

The reverse reaction to ammonia synthesis, the decomposition to nitrogen and hydrogen, is used in die nitriding of iron and canied out industiially at temperatures around 800 K and atmospheric pressure to produce surfacehardening. This dissolution reaction must also play a part in the synthesis of ammonia by the industiial process. The attempt to ninide non by reaction with nin ogen gas is vety slow under atmospheric pressure, presumably due to the stability of the nitrogen molecule. 

Like phase changes, chemical reactions tend toward a dynamic equilibrium in which, although there is no net change, the forward and reverse reactions are still taking place, but at matching rates. What actually happens when the formation of ammonia appears to stop is that the rate of the reverse reaction,... 

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 ... 

How do we get the temperature of the system to rise By adding heat. When we add heat, this equilibrium system reacts to reduce that stress, that is, to use up some of the added heat. It can use up heat in the reverse reaction, the decomposition of ammonia to hydrogen and nitrogen. When the substances written as products of the reaction (on the right side of the equation) react to produce more reactants (on the left side of the equation), we say that the reaction has shifted to the left. When the opposite process occurs, we say that the equilibrium has shifted to the right. Thus, raising the temperature on this system already at equilibrium causes a shift to the left some of the ammonia decomposes without being replaced. 

A = +14 cm3 mol-1 for both the forward and the reverse reaction. That this AV value is markedly less than the partial molar volumes of water and of ammonia (25 and 18 cm3 mol-1, respectively) indicates limiting dissociative (D) activation (133), as do the A values of close to +70JK-1mol-1 in both directions. Overall, the current situation with regard to thermal substitution at pentacyanoferrates(II) appears to be that an I,i mechanism can also operate for reactions of [Fe(CN)5(H20)]3-, whereas the D mechanism operates for all other [Fe(CN)5L]" complexes (134). 

Equilibrium. Forward and reverse reactions occurring at the same rate, resulting in a concentration of reactants. A + B C + D. Ammonia synthesis is an equilibrium reaction (N2 + 3H2 2NH3). 

However, attempts to make an aqueous solution of the base sodium amide would result in the formation of sodium hydroxide and ammonia. The amide ion is a strong base and abstracts a proton from water, a weak acid. The reverse reaction is not favoured, in that hydroxide is a weaker base than the amide ion, and ammonia is a weaker acid than water. Take care with the terminology amide the amide... 

The consequence of this is that an ester can react with ammonia to give an amide, but the reverse reaction does not occur simply treating amides with... 

Amide formation involved the same considerations. Thus, esters are readily converted into amides by treatment with ammonia (see Section 7.10). The intermediate anion has two potential leaving groups, alkoxide RO and amide NH2, and alkojdde is the better leaving group. The converse of this is that treatment of an amide with an alcohol does not lead to an amide we generate the same intermediate anion, so the reverse reaction, loss of alkoxide, predominates. 

The reaction involves formation of an imine through reaction of ammonia with the ketone, followed by reduction of this imine (see Section 7.7.1). As we noted earlier (see Section 15.1.1), nicotinamide coenzymes may also participate in imine reductions as well as aldehyde/ketone reductions, further emphasizing the imine-carbonyl analogy (see Section 7.7.1). The reverse reaction, removal of ammonia from glutamate, is also of importance in amino acid catabolism. 

At a first sight this could very well be an elementary biomolecular reaction with two molecules of ammonia combining to yield directly the four product molecules. From this principle, however, the reverse reaction would then also have to be an elementary reaction involving the direct combination of three molecules of hydrogen with one of nitrogen. Because such a process is rejected as improbable, the bimolecular forward mechanism must also be rejected. 

Lyases Decarboxylases Dehydratases Hydratases Add the elements of water, ammonia, or carbon dioxide across a double bond (or the reverse reaction)... 

In the discussion of reactions in Chapter 5, all reactions were written as complete reactions. Complete reactions are written with a single arrow pointing to the right (-> ), indicating reactants are converted into products. For complete reactions, reactants are converted into products until one of the reactants disappears. Many reactions are actually reversible reactions. Reversible reactions are written with a double arrow ( or Reversible reactions actually consist of two reactions called the forward reaction and the reverse reaction. The forward reaction represents the conversion of reactants into products, while the reverse reaction represents the conversion of products back to reactants. The reaction of hydrogen and nitrogen to form ammonia is a reversible reaction ... 

A remarkable reversal of the enyne system takes place if the enyne amines H2C=CHC=CNR2 are treated with potassium amide in liquid ammonia. The reaction must proceed through the butatrienyl amines H2C C=C=CHNR2 [185] ... 

The reaction is reversible since nitramine in aqueous solution combines with cyanic acid to reform nitrourea. Nitrourea is decomposed by gaseous ammonia, a reaction which, according to Watt and Makosky [63] proceeds as follows ... 

The first step is strongly endothermic and is the main hurdle to overcome in the hydrogenation of nitrogen to ammonia. Conversely, the reverse reaction, which is the dehydrogenation of diimide, is strongly exothermic. Therefore we may expect that diimide will have a pronounced tendency to revert to molecular nitrogen. This is in fact so and, at normal temperatures, diimide exists only as a transient intermediate that cannot be isolated. It is extremely reactive and readily transfers hydrogen to carbon-carbon multiple bonds ... 

As with the dissociation of acetic acid discussed in Section 4.2, the reaction of ammonia with water takes place only to a small extent (about 1%). Most of the ammonia remains unreacted, and we therefore write the reaction with a double arrow to show that a dynamic equilibrium exists between forward and reverse reactions. 

In general, whether the forward or reverse reaction is spontaneous depends on the temperature, pressure, and composition of the reaction mixture. Consider the Haber synthesis of ammonia ... 

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