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The Haber Process

Le Chatelier's Principle.

For a reversible reaction, Le Chatelier's principle states that

"The equilibrium position will respond
to oppose a change in the reaction conditions".

What this means in practice is

1. If you remove a product, the equilibrium mixture
changes to make more product. It tries to return to the
composition it had before the product was removed.
You can continue to remove more product until
all of the reactants have turned into product (useful!).

The reverse of 1 is also true.
If you remove a reactant the equilibrium changes
to make more reactant (this is generally not useful).

2. Heat may be treated as a reactant
(for an endothermic reaction)
or as a product (for an exothermic reaction).

If you remove heat from an exothermic reaction by cooling
it, the equilibrium will change to produce more product.
This will not only release more heat, but also produce more
of the chemical product that you want in the
equilibrium mixture. If you add heat to an exothermic reaction
by raising its temperature, the reverse will happen,
and you will get less product in the equilibrium mixture.
The opposite of 2 is true for an endothermic reaction.

3. For a reversible reaction involving gases,
increasing the pressure will change the equilibrium to make
more of the side of the reaction that has the smaller volume.

Decreasing the pressure will change the equilibrium to make
more of the side of the reaction that has the larger volume.

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