Ammonia

Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the formula NH₃. A stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pungent smell. It is widely used in fertilizers, refrigerants, explosives, cleaning agents, and is a precursor for numerous chemicals. Biologically, it is a common nitrogenous waste, and it contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to fertilisers. Around 70% of ammonia produced industrially is used to make fertilisers in various forms and composition, such as urea and diammonium phosphate. Ammonia in pure form is also applied directly into the soil.

Ammonia, either directly or indirectly, is also a building block for the synthesis of many chemicals. In many countries, it is classified as an extremely hazardous substance. Ammonia is toxic, causing damage to cells and tissues. For this reason it is excreted by most animals in the urine, in the form of dissolved urea.

Ammonia is produced biologically in a process called nitrogen fixation, but even more is generated industrially by the Haber process. The process helped revolutionize agriculture by providing cheap fertilizers. The global industrial production of ammonia in 2021 was 235 million tonnes. Industrial ammonia is transported by road in tankers, by rail in tank wagons, by sea in gas carriers, or in cylinders. Ammonia occurs in nature and has been detected in the interstellar medium.

Ammonia boils at −33.34 °C (−28.012 °F) at a pressure of one atmosphere, but the liquid can often be handled in the laboratory without external cooling. Household ammonia or ammonium hydroxide is a solution of ammonia in water.

The name ammonia is derived from the name of the Egyptian deity Amun (Ammon in Greek) since priests and travelers of those temples would burn soils rich in ammonium chloride, which came from animal dung and urine. Pliny, in Book XXXI of his Natural History, refers to a salt named hammoniacum, so called because of the proximity of its source to the Temple of Jupiter Amun (Greek Ἄμμων Ammon) in the Roman province of Cyrenaica. However, the description Pliny gives of the salt does not conform to the properties of ammonium chloride. According to Herbert Hoover's commentary in his English translation of Georgius Agricola's De re metallica, it is likely to have been common sea salt. In any case, that salt ultimately gave ammonia and ammonium compounds their name.

Traces of ammonia/ammonium are found in rainwater. Ammonium chloride (sal ammoniac), and ammonium sulfate are found in volcanic districts. Crystals of ammonium bicarbonate have been found in Patagonia guano.

Ammonia is found throughout the Solar System on Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto, among other places: on smaller, icy bodies such as Pluto, ammonia can act as a geologically important antifreeze, as a mixture of water and ammonia can have a melting point as low as −100 °C (−148 °F; 173 K) if the ammonia concentration is high enough and thus allow such bodies to retain internal oceans and active geology at a far lower temperature than would be possible with water alone. Substances containing ammonia, or those that are similar to it, are called ammoniacal.

Ammonia is a colourless gas with a characteristically pungent smell. It is lighter than air, its density being 0.589 times that of air. It is easily liquefied due to the strong hydrogen bonding between molecules. Gaseous ammonia turns to a colourless liquid, which boils at −33.1 °C (−27.58 °F), and freezes to colourless crystals at −77.7 °C (−107.86 °F). Little data is available at very high temperatures and pressures, but the liquid-vapor critical point occurs at 405 K and 11.35 MPa.