<P> If mineral acid is added to the acetic acid mixture, increasing the concentration of hydronium ion, the amount of dissociation must decrease as the reaction is driven to the left in accordance with this principle . This can also be deduced from the equilibrium constant expression for the reaction: </P> <Dl> <Dd> K = (CH 3 CO 2 −) (H 3 O +) (CH 3 CO 2 H) (\ displaystyle K = (\ frac ((\ ce (\ (CH3CO2 ^ - \) \ (H3O+ \)))) ((\ ce (\ (CH3CO2H \)))))) </Dd> </Dl> <Dd> K = (CH 3 CO 2 −) (H 3 O +) (CH 3 CO 2 H) (\ displaystyle K = (\ frac ((\ ce (\ (CH3CO2 ^ - \) \ (H3O+ \)))) ((\ ce (\ (CH3CO2H \)))))) </Dd> <P> If (H O) increases (CH CO H) must increase and CH 3CO − 2 must decrease . The H O is left out, as it is the solvent and its concentration remains high and nearly constant . </P>

Example of a reaction at chemical equilibrium in a cell