Chapter 6. Microscale Gas Chemistry:

Ammonia Information

A. Appearance

    Ammonia is a colorless gas with a sharp, irritating odor.  It is extremely soluble in water and is lighter than air.

B. Physical Properties of NH3

Ammonia, NH3
Atomic mass: 17.0306 g/mol
melting point -77.7 oC
boiling point -33.3 oC
C. History
     Ammonia was first isolated by Priestley in 1774 with the aid of a pneumatic trough filled with mercury instead of water.

D. Natural Abundance
     Ammonia is produced by the anaerobic decay of organic material.  Ammonia was the first complex molecule to be identified in interstellar space and solid NH3 makes up the rings on Saturn.

E. Industrial Production
     Prior to the 20th century, ammonia was made by destructive distillation of animal parts such as hoofs, horns, etc.  The common name for ammonia was “Spirits of Hartshorn.”  In 1913, Haber worked out a synthetic route to catalytically produce ammonia from the elements at high pressure and temperature.  The Haber process is still used today.

N2(g) + 3 H2(g) ---> 2 NH3(g)        DH = -92 kJ    DS = -199 J/K

F. Industrial Uses
     Ammonia production is the largest consumer of nitrogen and is the gateway compound to most other nitrogen compounds produced industrially.  Enormous quantities of ammonia are produced worldwide.  Much of the ammonia produced in the USA is used directly for fertilizer.  The figure below shows the various uses of ammonia.  The majority of all ammonia and ammonium nitrate producted is for use as fertilizer.  Approximately 70% of all NH3 produced is directly used for fertilizer.  Farmers inject the pressurized liquid ammonia into the soil.  Ammonia is so soluble in water and has such a high affinity for polar groups such as hydroxyl groups that the ammonia is almost instantly taken up by the soil and very little is lost to the atmosphere.

    Other important uses of ammonia include the production of nitric acid, use as a refrigerant, and use as a non-aqueous solvent.  Ammonia’s use as a refrigerant comes from the fact that it is a condensable liquid.  Ammonia is currently commonly used as the refrigerant in large industrial refrigerators and freezers.  Its main disadvantage in residential use stems from its toxicity should a leak in the system develop.  Liquid ammonia is also the most common, widely used non-aqueous solvent.  Its boiling point, -33.3 oC, requires that vessels be refrigerated or pressurized.  Ammonia is used in the manufacture of numerous other chemicals and products ranging from dyes to plastics.

G. Gas Density of NH3
      The density of NH3 is 0.6826 g/L at 25 oC and 1 atm.  This is about half that of air’s, thus it tends to rise in a still room.

H. Gas Solubility of NH3
     Ammonia is extremely soluble in water.  As much as 89.9 g dissolve per L at 0 oC.  This means that 1 mL of water will dissolve 1183 mL ammonia!  At 100 oC, the solubility drops to 7.4 g ammonia /100 mL H2O (113 volumes NH3 per 1 volume water.)

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