If pressure is increased, the ammonia reaction shifts in the direction
that decreases the total number of moles of gas and lowers the pressure.
If we dilute the reacting mixture by adding an inert gas such as
argon, but keep the total, pressure constant (which means that the
volume must increase), then Le Chatelier's principle predicts that
the ammonia equilibrium will shift in the direction that increases
the total number of moles of gas. More ammonia will dissociate.
We can arrive at the same prediction from the equilibrium - constant
Diluting an equilibrium mixture with an equal volume of argon gas
at fixed total pressure cuts each of the partial pressures of ,
in half-exactly the same effect as halving the pressure or doubling
The concentration ratio increases by a factor of 4,
and more ammonia dissociates until the concentration ratio again
is equal to the equilibrium constant:
= 670,000 .
Only if reactants and products contain the same number of moles
of gas will equilibrium be unaffected by pressure changes or dilution.