The concentration or pressure ratio
would decrease by a factor of (2)
(2) = 1/4, and would become smaller than the equilibrium constant,
would react until the imbalance was corrected and the concentration
ratio again was equal to .
Pressure changes have no effect if the total number of moles of
gas is unchanged during the reaction. The HCl synthesis would be
unaffected by an increase or decrease in external pressure.
These pressure effects are one example of an important general principle,
which, if understood, can save a lot of mathematics. This is Le
If external stress is applied to a system at equilibrium,
the equilibrium conditions will shift so as to compensate for, or
counteract, the stress.
Henri Louis Le Chatelier (1850 - 1936)