Le Chatelier's Principle
Simple Explanation
Le Chatelier's principle states that if a system at equilibrium is disturbed (by a change in concentration, pressure, or temperature), the equilibrium shifts in whichever direction partially counteracts that disturbance, settling into a new equilibrium.
Why Do We Need It?
This single principle predicts the direction an equilibrium will shift for almost any change you could make to a reaction system — it's the practical, predictive tool chemists use constantly, from industrial reactor design to understanding biological systems.
Why Does This Work?
Any disturbance to an equilibrium temporarily makes the forward and reverse rates unequal again — the system then naturally proceeds in whichever direction restores the rates to being equal, which happens to be the direction that partially undoes the disturbance (though it never fully returns to the exact original state).
Real-Life Example
Haemoglobin and oxygen transport
Haemoglobin in blood binds oxygen in the lungs and releases it in the body's tissues.
Haemoglobin + O₂ ⇌ oxyhaemoglobin is an equilibrium: high O₂ concentration in the lungs shifts it toward oxyhaemoglobin (loading up oxygen), while low O₂ concentration in tissues shifts it back, releasing oxygen exactly where it's needed — a direct, life-sustaining application of Le Chatelier's principle.
Practice
According to Le Chatelier's principle, what happens when a system at equilibrium is disturbed?
MediumCommon mistake
Thinking the equilibrium shift completely cancels out the disturbance, returning the system to exactly its original state — in reality, the shift only PARTIALLY offsets the change; the system reaches a new equilibrium position, not the original one.
Quick Review
- Le Chatelier's principle: a disturbed equilibrium shifts to partially counteract the disturbance.
- Applies to changes in concentration, pressure, and temperature.
- The system settles into a NEW equilibrium, not the original one.