The document discusses reversible reactions and the Haber process for producing ammonia from nitrogen and hydrogen. It notes that the Haber process uses high pressure of around 200 atmospheres, a temperature of 450°C, and an iron catalyst. At equilibrium, the reaction mixture is cooled to liquefy the ammonia, which is then separated from the recycled unreacted nitrogen and hydrogen for another cycle. The conditions aim to increase ammonia yield while maintaining a fast reaction rate and reasonable costs.

1. C7 Chemistry Reversible Reactions 09/05/11

2. Exothermic vs endothermic: 09/05/11 EXOTHERMIC – more energy is given out than is taken in (e.g. burning, respiration) ENDOTHERMIC – energy is taken in but not necessarily given out (e.g. photosynthesis)

3. Reversible Reactions 09/05/11 Some chemical reactions are reversible. In other words, they can go in either direction: If a reaction is EXOTHERMIC in one direction what must it be in the opposite direction? A + B C + D NH 4 Cl NH 3 + HCl e.g. Ammonium chloride Ammonia + hydrogen chloride For example, consider copper sulphate: Hydrated copper sulphate (blue) Anhydrous copper sulphate (white) + Heat + Water CuSO 4 + H 2 O CuSO 4 .5H 2 O

4. Reversible Reactions 09/05/11 When a reversible reaction occurs in a CLOSED SYSTEM (i.e. no reactants are added or taken away) an EQUILIBRIUM is achieved – in other words, the reaction goes at the same rate in both directions: More products Less products Less products More products A + B C + D Endothermic reactions Increased temperature: Decreased temperature: A + B C + D A + B C + D Exothermic reactions Increased temperature: Decreased temperature: A + B C + D A + B C + D

8. Uses of Ammonia 09/05/11 Nitrogen monoxide Ammonia is a very important chemical as it can be used to make plant fertilisers and nitric acid: More ammonia can then be used to neutralise the nitric acid to produce AMMONIUM NITRATE (a fertiliser rich in nitrogen). The trouble with nitrogen based fertilisers is that they can also create problems – they could contaminate our drinking water. Hot platinum catalyst Ammonia gas Oxygen Cooled Water and oxygen Nitrogen monoxide Nitric acid Ammonia + nitric acid Ammonium nitrate NH 3 + HNO 3 NH 4 NO 3