The Haber Process

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Ammonia
Ammonia is needed to produce fertiliser, ammoniate nitrate. Without manufacturing ammonia to make
fertiliser we wouldn't be able to make enough food to feed the population.
Process
Nitrogen is extracted directly from the air which contains 78% nitrogen. Hydrogen comes from digging
down deep enough you can get methane. This methane is reacted with steam to form carbon dioxide and
water. The water is then decomposed to for h2 hydrogen molecules.
The reactant enter the reaction vessel where an iron catalyst, a temperature of 450 degrees and an
atmospheric pressure of 200 is used to react some of the hydrogen and nitrogen to form ammonia.
Ammonia is formed as a gas but is cooled in a condenser, liquifies and is removed.
The unreacted hydrogen and mitrogen is recycled and fed back into the reaction vessel so nothing is
wasted.
[As the reaction is reversible the ammonia produced can decompose to form the reactants again which is
why ammonia is constantly removed to prevent it breaking back into the reactants.]
[[Iron catalyst increases the rate of reaction by lowering the activation energy so ammonia is
produced in a shorter time reducing industrial costs ]]
Temperature
Equillbrium considerations: In order to produce the most ammonia possible you need to shift the
position of the equilbrium right - ( in the direction of the product) so more product is being produced
than that is being broken back down. This will happen if you lower the temperature as it will respond
by giving out more heat and producing more ammonia. In the reaction the production of ammonia is
exothermic. Increasing the temperature makes it difficult to give out heat energy and so less
ammonia is produced. So more ammonia is produced at lower temperatures than higher
temperatures. There is a higher yield at lower temperatures ( more ammonia is produced). However
lowering the temperature also lowers the rate of reaction and so less hydrogen and nitrogen react to
form ammonia at lower temperatures. This is why we comprimise to a temperature of 450 degrees to
have a reasonable yield (reasonable amount of ammonia is produced) and reasonable rate of
reaction (produced quicker). Also at even higher temperatures ammonia will split back into hydrogen
and nitrogen.
Pressure
Equillibrium: If you look at the equation for the reaction we see there are 4 molecules on the left (two
nitrogen atoms = 1 molecule and 6 hydrogen atoms = 3 molecules) Whereas on the right there are just two
molecules of nitrogen. If you increase the pressure the reaction favours the one with the fewest molecules
and the equilibrium position moves right and so more ammonia is produced. Higher pressure makes a larger
yield of ammonia (more ammonia) as compressing the gas increases the concentration increases the chance
of succesful collisions and increases the rate of reaction. However a high pressure means stronger and more
expensive pipes and reaction vessel are needed so instead we use an atm of 200. This is also for safety as
buildings, reaction vessels may not be able to withstand higher pressure.

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Balance symbol equation to learn]
Production costs: Type of exam question you could get is what other factors do you need to
consider before deciding which temperatue/pressure to go for. Usally if both of these are mentioned
then its really about using your common sense. Factors to consider would be labour costs, price of
energy/electricity used to maintain high temperatures.…read more

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