 Nitrogen has a triple bond which is very strong. :N:::N:  Only at very high temperatures will it react with oxygen.  This occurs in the combustion engine and toxic oxides of nitrogen (NO, NO 2 ) are produced.

 Nitrogen is an essential element for living things – it is present in proteins.  Plants absorb nitrogen in the form of nitrates (NO 3 - ).  Nitrates get into the soil through the action of lightning and decomposing micro-organisms.  Some plants (often called legumes) have nitrogen fixing bacteria in their root nodules

 Because nitrates are very soluble they are easily leached from soils, and added back through fertilisers (P and K are also present).  Animals get their nitrogen containing compounds through the food chain.

 Farmyard manure is an organic fertiliser containing compounds that can be converted by bacteria in the soil to nitrates.  A commonly used artificial fertiliser is ammonium nitrate, which is made from ammonia gas and nitric acid. NH 3(g) + HNO 3(aq)  NH 4 NO 3(aq)  Urea is another one and is produced by reacting ammonia gas and carbon dioxide gas. 2NH 3(g) + CO 2(g)  CO(NH 2 ) 2(s) + H 2 O (l)

 When too much fertiliser is applied to pastures, it can wash into streams and lakes.  Increased nitrate concentration causes algae to multiply rapidly and cover the lake.  This restricts the light available to aquatic plants.  Photosynthesis is reduced and so oxygen in the water is depleted.  When algae die, the dissolved oxygen is used up and fish die.  This process is called eutrophication.

 Is a colourless gas, less dense than air, very soluble in water and with a pungent smell.  Turns litmus paper blue.  Is a weak Bronsted-Lowry base

 Nitrogen is fractionally distilled from air.  Hydrogen is obtained by ‘steam reforming’: CH 4(g) + H 2 O (g) ⇌ 3H 2(g) + CO (g) Conditions: 750°C, 30 atm, Ni catalyst. CO then reduces unreacted steam: CO (g) + H 2 O (g) ⇌ H 2(g) + CO 2(g)  Haber Reaction: N 2(g) + 3H 2(g) ⇌ 2NH 3(g) ∆ H = -92 kJmol -1 Conditions: °C, 200atm, Fe catalyst

 Small quantities of ammonia gas can be produced by heating an ammonium salt with an alkali such as calcium hydroxide. Ca(OH) 2(s) + 2NH 4 Cl (s) → CaCl 2(s) + 2H 2 O (g) + 2NH 3(g) calcium ammonium calcium water ammonia hydroxide chloride chloride  Water vapour can be removed by passing the gas through a drying tower containing calcium oxide.

 Ammonia is also used in the production of HNO 3 by catalytic oxidation of air using a platinum/rhodium catalyst at 900 o C.  The overall reaction is: NH 3(g) + 2O 2(g)  HNO 3(g) + H 2 O (g)  Nitric acid is used to make ammonium nitrate (fertiliser and explosive), nylon and other explosives.

 Oxides of carbon and nitrogen are produced in the combustion of fossil fuels. Without treatment they can cause photochemical smog.  Catalytic converters (fitted to the exhaust of new cars in Europe) speeds up the following reactions: 2CO (g) + O 2(g) → 2CO 2(g) carbon oxygen carbon monoxide dioxide 2NO (g) + 2CO (g) → N 2(g) + 2CO 2(g) nitrogen (I) carbon nitrogen carbon oxide monoxide dioxide