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. Th . . .
Further to this the use of chemical fertilisers also affects the global nitrogen cycle, pollutes groundwater and increases the level of atmospheric nitrogen dioxide - a potent "greenhouse" gas. With regard to temperature, the reaction moving to the right is exothermic i. Raffles Institute Media Networking Club - Web page - 4 June 2000 4. After hundreds of experiments Haber discovered that a fast enough reaction with a high enough yield of ammonia would occur with a pressure between 200 and 400 atmospheres and at a temperature between 670K and 920K in the presence of a catalyst of iron (in the form of iron filings to increase its active surface area) plus a few percent of oxides of potassium and aluminium. Unfortunately experimentation showed that, as temperature approached the point at which the speed of the reaction was sufficient to produce a viable reaction the amount of ammonia produced was so low that the reaction was still unfeasible on as an industrial process. 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. The University of Edinburgh 2000 . Though both of the above projects are far from complete they do demonstrate a commitment to making the Haber Process redundant and it is fairly certain that even if these avenues of research prove to be unsuccessful others will be explored until an alternative is found. At extremely high temperature the nitrogen molecule will dissociate and so, as the temperature approaches this point the rate at which the reaction to the right occurs and therefore the speed with which equilibrium is reached increases rapidly. As a result funding is now being allocated to finding alternatives to this process. As a result of this work is now underway to both try to solve the problem of the high energy consumption of the Haber Process and to reduce our reliance on chemical fertilisers. This has enabled research to commence on low energy methods of producing ammonia. towards the product required) is favoured by an increase in pressure. This process was first demonstrated in 1909 and patented as the Haber Process in 1910 (3).
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