Once a system has reached equilibrium, the relative concentrations or pressures of the species in the reaction do not change. However, if you disturb the system in some way, the equilibrium will adjust until a new equilibrium is established. LeChatlier's Principle states that "If a system at equilibrium is disturbed the system will, if possible, shift to partially counteract the change"

Possible disturbances include

• Adding or removing a species
• Changing the temperature
• For gases, changing the pressure
• For electrochemical cells, changing the potential across the cell.

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