50. Le Chatelier’s Principle: Position of Equilibrium

Le Chatelier’s Principle: Position of Equilibrium

Based on the video, here are the notes on Le Chatelier’s Principle and how changes in conditions affect the position of equilibrium in reversible reactions.

1. Core Concept

• Le Chatelier’s Principle: If you change the conditions of a reversible reaction at equilibrium, the system will shift its position of equilibrium to counteract or oppose that change.

• Purpose: This principle allows us to predict how a system will respond to changes in temperature, pressure, and concentration.

2. Effect of Temperature

To predict the shift, you must know if the forward reaction is exothermic or endothermic.

• Decrease Temperature: The equilibrium shifts in the exothermic direction to release heat and warm the system back up.

• Increase Temperature: The equilibrium shifts in the endothermic direction to absorb the extra heat and cool the system down.

• Example: In the production of ammonia, the forward reaction is exothermic. Decreasing the temperature shifts equilibrium to the right, producing more ammonia.

3. Effect of Pressure (Gases only)

Pressure is related to the number of gas molecules in the system.

• Increase Pressure: The equilibrium shifts to the side with the fewest molecules of gas to reduce the pressure.

• Decrease Pressure: The equilibrium shifts to the side with the most molecules of gas to increase the pressure.

• Example: N₂ + 3H₂ ⇌ 2NH₃. There are 4 molecules on the left and 2 on the right. Increasing pressure shifts equilibrium to the right.

4. Effect of Concentration

• Increase Reactant Concentration: The equilibrium shifts to the right (towards products) to use up the extra reactants.

• Decrease Product Concentration: The equilibrium shifts to the right to replace the removed products.

• In short: The system always shifts to the opposite side of whatever you added to oppose the change.

5. Summary Table