Ammonium nitrate, dissolution

See an animation of Enthalpy and Entropy Changes in Ammonium Nitrate Dissolution at http // brookscole.com/chemistry/ joesten4... 

The impurities in ordinary iron assist dissolution in acid, and are responsible for the characteristic smell of the hydrogen from this source.) In dilute nitric acid, ammonium nitrate is formed ... 

Ammonium nitrate has a negative heat of solution in water, and can therefore be used to prepare freezing mixtures. Dissolution of ammonium nitrate in anhydrous ammonia, however, is accompanied by heat evolution. In dilute solution the heat of neutralization of nitric acid using ammonia is 51.8 kj/mol (12.4 kcal/mo). 

A process that releases heat into the surroundings is called an exothermic process. Most common chemical reactions—and all combustions, such as those that power transport and heating—are exothermic (Fig. 6.8). Less familiar are chemical reactions that absorb heat from the surroundings. A process that absorbs heat is called an endothermic process (Fig. 6.9). A number of common physical processes are endothermic. For instance, vaporization is endothermic, because heat must be supplied to drive molecules of a liquid apart from one another. The dissolution of ammonium nitrate in water is endothermic in fact, this process is used in instant cold packs for sports injuries. 

An instant ice pack for first-aid treatment uses the endothermic nature of the dissolution of an ionic salt in water to provide cold therapy. Two typical materials that absorb heat as they dissolve in water are ammonium nitrate and ammonium chloride ... 

The standard enthalpy of reaction for the dissolution of ammonium nitrate in water can be calculated using the enthalpies of formation for reactants and products ... 

Thus, the enthalpy change is about half that for the dissolution of ammonium nitrate in water. An estimate of the temperature achieved by the ice pack can be calculated knowing the amounts of water and salt present and assuming that the salt dissolves completely. 

Manufacturers take advantage of endothermic dissolution to produce cold packs that athletes can use to treat injuries. One type of cold pack contains water and a salt, such as ammonium nitrate, in separate compartments. When you crush the pack, the membrane that divides the compartments breaks, and the salt dissolves. This dissolution process is endothermic. It absorbs heat for a short period of time, so the cold pack feels cold. Figure 5.8 shows how a cold pack works. 

When a solute is dissolved in a solvent, heat may either be evolved (as with sulfuric acid in water, where strong heating is observed) or absorbed (as with ammonium nitrate in water, where strong cooling is observed). Thus the dissolution may be either exothermic or endothermic, and the standard molar enthalpy of solution, is then either negative or positive. The sign of AsaJl°... 

Dissolution of ammonium nitrate (NH NO ) is an endothermic process. When ammonium nitrate is dissolved in a beaker placed on wood with a few water droplets, the beaker sticks to the wood due to the. formation of ice. 

Nobel developed gelatinous dynamite in 1875 by making a jelly from the dissolution of a collodion-type nitrocotton in NG, producing a more powerful explosive than the straight dynamite and one that proved to be safer. Later ammonium nitrate was also used in dynamite, which made it even safer and less expensive to produce. 

FIGURE 8.22 The exothermic dissolution of lithium chloride (left) is shown b> the rise in temperature above that of the original water (center) in contrast, ammonium nitrate (right) dissolves endothermically. 

Tablets with aspirin and codeine HPLC Dissolution C-18(30 C) Acetonitrile-buffer (45 55) buffer-2.2 g DSC and ammonium nitrate 0.8 g/550 ml water 254 nm USP23 [5]...

Ammonium molybdate (0-25m for molybdenum). " Dissolve 44 2 g ammonium molybdate, (NH4)6Mo7024.4H20, in a mixture of 60 ml concentrated ammonia and 40 ml water. Add 120 g ammonium nitrate and after complete dissolution dilute the solution to 1 litre. Before use, the solution, to which the reagent is added, must be made acid by adding nitric acid. 

NOJ(aqf). This includes solid ammonium nitrate, the water in which it dissolves, and the aquated ions that are the products of the dissolution process. The surroundings include the flask or beaker in which the system is held, the air above the system, and other neighboring materials. The dissolution of ammonium nitrate is spontaneous after any physical separation (such as a glass wall or a space of air) between the water and the ammonium nitrate has been removed. 

On the other hand, when ammonium nitrate (NH4N03) dissolves in water, the solution gets colder and the temperature goes down. Therefore, the dissolution process of ammonium nitrate is endothermic (Figure 7). 

When the bag is squeezed, the inner pouch breaks and ammonium nitrate, NH4N03, and water mix. Since the dissolution of ammonium nitrate is endothermic, the water temperature decreases to about 5°C. 

The excess ammonium nitrate dissolves in the water produced in the reaction, (b) The dissolution process is very endothermic. If the flask is placed on a wet wooden block, the water freezes and attaches the block to the flask. 

Another factor, related to the disorder of reactants and products, also plays a role in determining spontaneity. The dissolution of ammonium nitrate, NH4NO3, in water is spontaneous. Yet a beaker in which this process occurs becomes colder (see Figure 15-2). 

In this case, the assnmption that spontaneous processes always decrease a system s energy fails. Experience tells us that ice melts spontaneously above 0°C even though the process is endothermic. Another example that contradicts our assumption is the dissolution of ammonium nitrate in water ... 

Ammonium chloride and ammonium nitrate salts can be added to boiler feed water to reduce effluent pH and minimize silica dissolution (84). 

Figure 10.22 shows the calculated ammonium and nitrate for a closed system as a function of its RH. The ammonium nitrate concentration increases by a factor of 8 in this example as the RH increases from 65% to 95%. Further increases of the RH will lead to the complete dissolution of practically all the available nitric acid to the particulate phase (see also Chapter 7). 

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