Le Chatelier's Principle
Definition and meaning of Le Chatelier's Principle in chemistry.
Le Chatelier's Principle states that when a system at equilibrium is subjected to a change in conditions (temperature, pressure, or concentration), the system will shift in a direction to counteract that change and restore equilibrium.
In more detail
The principle describes how chemical equilibria respond to external stresses. When you increase the concentration of reactants, the system shifts toward products to consume the excess. If you increase temperature in an endothermic reaction, the system shifts toward products to absorb the added heat. Increasing pressure in a gas-phase system favors the side with fewer moles of gas. This principle predicts equilibrium behavior and is essential for optimizing chemical processes without detailed calculations.
Key facts
| Field | Physical Chemistry |
|---|---|
| Discovered | 1884 by Henri Le Chatelier |
| Key Variables | Temperature, pressure, concentration, volume |
| Core Principle | Systems shift to oppose external disturbances |
In the equilibrium N2(g) + 3H2(g) ⇌ 2NH3(g), increasing pressure shifts the equilibrium toward ammonia because the product side has fewer moles of gas (2 moles vs. 4 moles on the reactant side). This reduces total pressure, counteracting the applied stress.
Frequently asked questions
Does Le Chatelier's Principle apply to all equilibria?
Yes, it applies universally to all dynamic equilibria in chemistry, including gas-phase, aqueous solution, and heterogeneous equilibria.
How can you use this principle to increase product yield?
By shifting equilibrium toward products through temperature, pressure, or concentration changes, you increase yield in industrial processes like the Haber process for ammonia synthesis.