Le Chatelier's Principle: Unraveling the Effect of Concentration on Equilibrium

Introduction

Welcome, NEET aspirants! Chemical equilibrium is a dynamic state where forward and reverse reaction rates are equal. But what happens when we disturb this delicate balance? This is where Le Chatelier's Principle comes in handy! It 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. Today, we'll dive deep into one of the most common stresses: the effect of changing concentration.

Core Concept: How Concentration Changes Affect Equilibrium

Changes in the concentration of reactants or products directly impact the equilibrium position. The system always tries to counteract the change you impose.

• Increasing the concentration of a reactant: The system will try to consume the added reactant. This means the equilibrium will shift in the forward direction (towards the products) to produce more products and reduce the excess reactant.

  • Example: A + B ⇌ C. If you add more A, the reaction shifts right to make more C.

• Decreasing the concentration of a reactant: The system will try to replenish the removed reactant. This means the equilibrium will shift in the reverse direction (towards the reactants) to form more reactants.

  • Example: A + B ⇌ C. If you remove some A, the reaction shifts left to make more A.

• Increasing the concentration of a product: The system will try to consume the added product. This means the equilibrium will shift in the reverse direction (towards the reactants) to reduce the excess product.

  • Example: A + B ⇌ C. If you add more C, the reaction shifts left to make more A and B.

• Decreasing the concentration of a product: The system will try to replenish the removed product. This means the equilibrium will shift in the forward direction (towards the products) to form more products.

  • Example: A + B ⇌ C. If you remove some C, the reaction shifts right to make more C.

Important Note: The addition or removal of pure solids or pure liquids does NOT affect the equilibrium position, as their concentrations remain constant and are not included in the equilibrium expression (K_c or K_p).

Solved Example

Consider the Haber-Bosch process for ammonia synthesis: N₂(g) + 3H₂(g) ⇌ 2NH₃(g)

1. If the concentration of N₂(g) is increased: The equilibrium will shift to the right (forward direction) to consume the added N₂. This will lead to an increase in the concentration of NH₃ and a decrease in H₂.
2. If the concentration of NH₃(g) is decreased (e.g., by liquefaction): The equilibrium will shift to the right (forward direction) to replenish the removed NH₃. This enhances the yield of ammonia.

NEET Trick

Think of it as the system trying to 'undo' what you did. If you add something, it shifts away from it. If you remove something, it shifts towards it. Simple! Just remember: Shift AWAY from what's ADDED, and TOWARDS what's REMOVED.

Quick Recap

• Le Chatelier's Principle: System counteracts stress.
• Increase Reactant: Shift Right (Forward).
• Decrease Reactant: Shift Left (Reverse).
• Increase Product: Shift Left (Reverse).
• Decrease Product: Shift Right (Forward).
• Pure Solids/Liquids: No effect on equilibrium position.