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Summary Ieb Haber Process Notes
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Summary of 3 pages for the course Physical Sciences at 12th Grade (Haber Process notes)
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Haber ProcessThe Haber Process combines nitrogen from the air with hydrogen derived mainly from natural gas (methane) into
ammonia. The reaction is reversible and the production of ammonia is exothermic
𝑁2 (𝑔) + 3𝐻2 (𝑔) = 2𝑁𝐻3 (𝑔) ∆𝐻 = −92𝑘𝐽𝑚𝑜𝑙 −1
Yield:
A measure of the extent of a reaction, generally measured by
comparing the amount of product against the amount of product
that is possible
𝑎𝑐𝑡𝑢𝑎𝑙
% 𝑦𝑖𝑒𝑙𝑑 =
𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙
Ammonia + Water
𝑁𝐻3 + 𝐻2 𝑂 = 𝑁𝐻4+ (𝑎𝑞) + 𝑂𝐻 −
𝐾𝑤 = [𝑂𝐻 − ][𝐻+ ] = 10−14
Some notes on the conditions
The catalyst
The catalyst is actually slightly more complicated than pure iron. It has potassium hydroxide added to it as a
promoter - a substance that increases its efficiency.
The pressure
The pressure varies from one manufacturing plant to another but is always high. You can't go far wrong in an exam
quoting 200 atmospheres.
Recycling
At each pass of the gases through the reactor, only about 15% of the nitrogen and hydrogen converts to ammonia.
(This figure also varies from plant to plant.) By continual recycling of the unreacted nitrogen and hydrogen, the
overall conversion is about 98%
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.
Avogadro's Law says that equal volumes of gases at the same temperature and pressure contain equal numbers of
molecules. That means that the gases are going into the reactor in the ratio of 1 molecule of nitrogen to 3 of
hydrogen.
That is the proportion demanded by the equation.
In some reactions you might choose to use an excess of one of the reactants. You would do this if it is particularly
important to use up as much as possible of the other reactant - if for example it was much more expensive. That
doesn't apply in this case.
There is always a down-side to using anything other than the equation proportions. If you have an excess of one
reactant there will be molecules passing through the reactor which can't possibly react because there isn't anything
for them to react with. This wastes reactor space - particularly space on the surface of the catalyst
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