Revise: EquilibriaFactors affecting equilibrium position

Once equilibrium has been established, chemists can control certain reaction conditions to influence the position of the equilibrium.

Altering the reaction conditions can result in the yield of products increasing, and the process being more profitable.

Le Chatlelier’s principle states that if a system at equilibrium is subjected to any change, the system will adjust itself to counteract the applied change.

There are a number of factors that can be changed.

Concentration

Adding a chemical that is present on either side of the equation will cause a shift in the position of the equilibrium, as the system adjusts to counteract the change.

Consider the following equilibrium:

If hydrochloric acid was added to the equilibrium mixture, both hydrogen ions (H⁺) and chloride ions (Cl^-) are being added.

Hydrogen ions are on the right hand side of the equilibrium, therefore the equilibrium will shift to the left hand side to compensate, resulting in a higher concentration of reactants.

Adding sodium hydroxide (NaOH) will also affect the position of the equilibrium.

While neither sodium ions (Na⁺) or hydroxide ions (OH^-) are present on either side, the hydroxide ions will remove H⁺ ions and the equilibrium will shift to the right hand side to replace the hydrogen ions that were removed.