Shifting the Position of Equilibrium

Introduction

• In a chemical reaction, dynamic equilibrium is established when the rates of the forward and reverse reactions are equal.
• Le Chatelier's principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium will shift to counteract the change and reestablish a new equilibrium.

Changing Reaction Conditions

Several factors can change the position of equilibrium in a reversible reaction:

• Concentration: Altering the concentration of reactants or products can shift the equilibrium. Increasing the concentration of a reactant will push the equilibrium towards the product side, and vice versa.

• Temperature: Changing the temperature can also affect equilibrium. In exothermic reactions (those that release heat), increasing the temperature will shift the equilibrium in the reverse direction to absorb the excess heat. In endothermic reactions (those that absorb heat), increasing the temperature will shift the equilibrium in the forward direction to counteract the temperature rise.

• Pressure (for gases): For reactions involving gases, changing the pressure can influence the equilibrium position. Increasing the pressure will shift the equilibrium towards the side with fewer gas molecules to reduce the pressure, and decreasing the pressure will shift it towards the side with more gas molecules.

Le Chatelier's Principle

• Le Chatelier's principle can be summarised as follows:
  • If you disturb a system at equilibrium by changing the conditions, the system will respond in a way that tends to counteract the disturbance and restore equilibrium.
• It's like a see-saw: if you add weight to one side, the see-saw tilts to balance the weights.

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Shifting the Position of Equilibrium

Examples

• Concentration Change: If you increase the concentration of one reactant, the equilibrium will shift towards the formation of more products to balance the concentrations.

• Temperature Change: In an exothermic reaction, increasing the temperature will shift the equilibrium towards the reactants to absorb excess heat. In an endothermic reaction, increasing the temperature will shift it towards the products to counteract the temperature rise.

• Pressure Change: For a reaction involving gases, increasing the pressure will shift the equilibrium towards the side with fewer gas molecules, and decreasing the pressure will shift it towards the side with more gas molecules.

Conclusion

• Le Chatelier's principle explains how a system at equilibrium responds to changes in concentration, temperature, and pressure.

• By shifting the equilibrium position, the system counteracts the change and reestablishes a new equilibrium that maintains dynamic balance in the reaction.