The Haber Process
Chemistry - Pressure.
2) Pressure of 200 atm (200 atmospheres).
Why is such a high pressure used?
+ hydrogen ammonia ( + heat).
N2(g) + 3H2(g) 2NH3(g) ( + heat).
If we look at the reaction, the reactants and products are gases.
One mole of any gas occupies a volume of 24,000 cm3.
On the left
side of the equation,
there is one mole of nitrogen, and three moles of hydrogen.
The total is four moles of reactant.
(If you don't know why there are 3 moles of hydrogen
and 1 mole of nitrogen, see moles).
On the right
side of the equation (the product),
there are two moles of ammonia.
moles of reactant give
two moles of product.
Since one mole of any gas takes up the same volume,
the volume of product is only half the volume of reactants.
Increasing the pressure (from Le Chatelier's Principle)
makes the equilibrium mixture have more ammonia.
This is what we want!
What effect does pressure have on
As we can see, increased pressure also
increases the reaction rate. Again, this is what we want!
Why not increase the pressure to 1,000
and get lots of ammonia really quickly?
the real world, it all comes down to
Building high pressure chemical plant is expensive.
Running the reaction at about 200 atm gives
the highest return (the biggest profit) on investment capital
(the amount of money you spend to set up the whole thing).
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