14. Chemical Equilibrium   Previous PageNext Page
       Factors Affecting Equilibrium

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 expression.

Diluting an equilibrium mixture with an equal volume of argon gas at fixed total pressure cuts each of the partial pressures of , , and in half-exactly the same effect as halving the pressure or doubling the volume.


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.

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