ammonia ( + heat).N2(g) + 3H2(g)
2NH3(g) ( +
heat).gcsescience.com 7 gcsescience.com
Chemistry - Pressure.
The
industrial
conditions are
2) Pressure of 200 atm (200
atmospheres).
Why is such a high pressure used?
nitrogen
+ 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.
So, four
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
reaction
rate?
As we can see, increased pressure also
increases the reaction rate.
Again, this is what we
want!
Q.
Why not increase the pressure to 1,000
atm,
and get lots of ammonia really
quickly?
A. In
the real world, it all comes down to
money.
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).
Links
Reversible Reactions
Revision Questions
gcsescience.com The Periodic Table Index Haber Process Quiz gcsescience.com
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