Le Chatelier's Principle
This principle states that if a change of condition is applied to a system in equilibrium, the system will shift in a direction that relieves the stress. Here's how it applies to adding a substance:
1. Adding a Reactant:
* Shift: The reaction will shift to the right (towards the product side) to consume the added reactant. This is because the system wants to reduce the concentration of the added reactant.
Example: Consider the reaction:
N₂(g) + 3H₂(g) ⇌ 2NH₃(g)
If we add more nitrogen (N₂), the equilibrium will shift to the right to produce more ammonia (NH₃) and consume the added nitrogen.
2. Adding a Product:
* Shift: The reaction will shift to the left (towards the reactant side) to consume the added product. The system aims to reduce the concentration of the added product.
Example: In the same ammonia reaction, if we add more ammonia (NH₃), the equilibrium will shift to the left to form more nitrogen (N₂) and hydrogen (H₂) and consume the added ammonia.
Important Considerations:
* Phase: The addition of a substance only affects the equilibrium if it is in the same phase as the reactants and products. Adding a solid to a liquid-phase reaction won't significantly shift the equilibrium.
* Stoichiometry: The extent of the shift depends on the stoichiometry of the reaction. If the reaction involves more moles of a particular substance, adding that substance will have a greater impact on the equilibrium shift.
In Summary
Adding a substance to a reversible reaction will cause the equilibrium to shift in a direction that reduces the concentration of the added substance. This is a fundamental principle used to understand and predict how chemical reactions respond to changes in their environment.
