The Haber Process
Haber Process
This is the process by which ammonia (NH3) is produced. The equation for this reaction is...
The symbol that you see in the middle means it is a reversible reaction, so the product can decompose back into the reactants. So optimum conditions must be selected to get the greatest yield. When the forward and backward reactions are the same, it is said to be in a state of dynamic equilibrium.
The position of this dynamic equilibrium can be moved forward by changing the conditions the reaction is done in. This follows Le Chatelier's Principle which says changes to a system in equilibrium will move it in an opposite direction.
| Condition | Effect |
|---|---|
| Pressure | Increasing this will improve the yield because the forward reaction reduces pressure. However, putting up the pressure too far is impractical and becomes too expensive because special instruments must be used to withstand the forces. |
| Temperature | A higher yield can be obtained by using a low temperature since the forward reaction produces heat, but this also will make the reaction slower, and less profitable so a temperature of about 450°C is used. |
| Catalyst | The haber process makes use of iron to speed up the reaction - but this doesn't improve the yield. To discover more about reaction rates, see rates of reaction |
The conditions of the Haber process must be finely balanced to reach a combination of highest yield and fastest reaction, this is very important because getting this right will make sure this industrial process is as profitable as possible.
Fertilisers
Ammonia is used in the production of fertilisers. A nitrogenous fertilisers is manufactured by neutralising ammonia with nitric acid.
nitric acid + ammonia ® ammonium nitrate
HNO3 (aq) + NH3 (aq) ® NH4NO3 (aq)
These fertilisers promote growth of plants, but this can cause problems...
Nitrates are very soluble, and are washed out of soils by rain, where they may travel to a lake, river, pond etc. The fertiliser causes a large boom in plant growth, but this boom is followed by a fall in plant life. All of this dead material causes decay by bacteria that use up the oxygen in the water and this means aquatic animals that rely on oxygen in the water will die.