In the absence of a catalyst the reaction is so slow that virtually no reaction happens in any sensible time. The catalyst ensures that the reaction is fast enough for a dynamic equilibrium to be set up within the very short time that the gases are actually in the reactor.
When the gases leave the reactor they are hot and at a very high pressure. Ammonia is easily liquefied under pressure as long as it isn't too hot, and so the temperature of the mixture is lowered enough for the ammonia to turn to a liquid.
The nitrogen and hydrogen remain as gases even under these high pressures, and can be recycled. If this is the first set of questions you have done, please read the introductory page before you start. A brief summary of the Haber Process The Haber Process combines nitrogen from the air with hydrogen derived mainly from natural gas methane into ammonia. A flow scheme for the Haber Process looks like this: Some notes on the conditions The catalyst The catalyst is actually slightly more complicated than pure iron.
The pressure The pressure varies from one manufacturing plant to another, but is always high. Explaining the conditions The proportions of nitrogen and hydrogen The mixture of nitrogen and hydrogen going into the reactor is in the ratio of 1 volume of nitrogen to 3 volumes of hydrogen. That is the proportion demanded by the equation. The temperature Equilibrium considerations You need to shift the position of the equilibrium as far as possible to the right in order to produce the maximum possible amount of ammonia in the equilibrium mixture.
The forward reaction the production of ammonia is exothermic. Rate considerations The lower the temperature you use, the slower the reaction becomes. The pressure Equilibrium considerations Notice that there are 4 molecules on the left-hand side of the equation, but only 2 on the right.
Rate considerations Increasing the pressure brings the molecules closer together. Economic considerations Very high pressures are very expensive to produce on two counts. The compromise atmospheres is a compromise pressure chosen on economic grounds.
The catalyst Equilibrium considerations The catalyst has no effect whatsoever on the position of the equilibrium. Rate considerations In the absence of a catalyst the reaction is so slow that virtually no reaction happens in any sensible time. Separating the ammonia When the gases leave the reactor they are hot and at a very high pressure. The Haber process for making ammonia provides a useful example of how this works:.
Controlling temperature. If the temperature is increased, the equilibrium position moves in the direction of the endothermic reaction. This means it moves to the left in the Haber process. You might think that a low temperature is chosen, moving the equilibrium position to the right and making more ammonia. However, the rate of reaction is low at low temperatures. This is:. Controlling pressure. If the pressure is increased, the equilibrium position moves in the direction of the fewest molecules of gas.
This means it moves to the right in the Haber process. You might think that a very high pressure is chosen to move the equilibrium position to the right, making more ammonia. However, it is expensive to achieve very high pressures. The abundance of synthetic fertiliser has led to a decrease in guano harvesting around the world, consequently leading to fewer seabirds becoming extinct and less damage to cave ecosystems since guano trade often caused bats to leave their roost.
Another consequence of the Haber Process is how efficient agriculture has become. Shockingly, the population has increased by almost 5x since the s. The Haber Process has directly led to the situation the world is in, from the greenhouse emissions due to the much larger carbon footprint of our generation, to the laws put in place limiting childbirth and arguably the rights of humans all around the world. During the First World War, Germany required high deposits of nitrates to form explosives.
The Allies had access to large sodium nitrate deposits in Chile but Germany had nothing. The Haber Process allowed the Germans to produce weapons from thin air, arguably helping Germany with their journey to the Second World War as well as directly killing many during the first.
During World War 2, the Nazis used hydrogen cyanide Zyklon B to murder minorities in the gas chambers and used ammonia to safely neutralise the toxic gas. These examples may be from long ago, but ammonium-nitrate based explosives are still used all around the world today.
They were used in the Sterling Hall bombing in Wisconsin, ; the Oklahoma City bombing, ; the Delhi and Oslo bombings, ; and even as recently as during the Hyderabad blasts.
The Haber Process and the ability to easily produce ammonia has not only resulted in cheaper yields but has directly caused deaths all around the world ever since its discovery.
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