1. The Haber Process
During the first decade of the twentieth century the world-wide demand for ammonia for use in fertilisers (in the form of nitrates) and in the production of explosives for use in mining and warfare could only be satisfied on a large scale from deposits of guano in Chile (2). Though this deposit was of huge size (approximately five feet thick and 385 kilometres long) it represented a rapidly depleting resource when compared to world-wide demand. As a result of this there was much research into how ammonia could be produced from atmospheric nitrogen. The problem was eventually solved by Fritz Haber (1868 - 1934) in a process which came to be known as the "Haber Process" or the "Haber - Bosch Process".
Haber developed a method for synthesising ammonia utilising atmospheric nitrogen and had established the conditions for large scale synthesis of ammonia by 1909 and the process was handed over to Carl Bosch for industrial development (1). the reaction is a simple equilibrium reaction which occurs in gaseous state as follows;
N2 (g) + 3H2 (g) = 2NH3 (g) heat of enthalpy = -92.6 kJ/mol
In predicting how to obtain the highest yield from this reaction we must refer to Le Chatlier's Principle. This states that for an equilibrium reaction the equilibrium will work in the opposite direction to the conditions forced upon it. The conditions most pertinent to the above reaction are temperature and pressure.
The pressure exerted by any gas or mixture of gasses in an enclosed space is directly proportional to the number of atoms or molecules of gas regardless of their size or molecular mass. Reference to the above reaction shows that, as the reaction moves to the right the number of molecules and hence the pressure decreases. Therefore the reaction moving to the right (i.e. towards the product required) is favoured by an increase in pressure.
With regard to temperature, the reaction moving to the right...