Le Chatelier's Principle Quiz

Le Chatelier's Principle

• Le Chatelier's Principle describes how an equilibrium system responds to external stress.
• The system shifts in a way that opposes the applied stress, aiming to re-establish equilibrium.

Stresses on Equilibrium

• Change in Concentration:
  • Adding a reactant or product shifts the equilibrium to consume the added substance.
  • Removing a reactant or product shifts the equilibrium to replenish the removed substance.
  • This applies only to gaseous or aqueous components, not solids or liquids.
  • Increased reactant concentration increases the rate of the reaction consuming it, thus shifting the equilibrium.
• Change in Volume/Pressure (for gaseous systems):
  • Decreasing volume (increasing pressure) shifts the equilibrium to the side with fewer moles of gas to decrease pressure.
  • Increasing volume (decreasing pressure) shifts the equilibrium to the side with more moles of gas to increase pressure.
  • This stems from the change in concentration due to volume changes which are larger on the side with more moles of gas, shifting equilibrium.
• Change in Temperature:
  • Increasing temperature favors an endothermic reaction (heat is absorbed).
  • Decreasing temperature favors an exothermic reaction (heat is released).
  • Increasing temperature increases both forward and reverse reaction rates, but the endothermic reaction rate increases more, shifting the equilibrium.
  • Temperature change is the only stress that alters the equilibrium constant (K).
    • Higher temperature favors the endothermic direction, increasing K.
    • Lower temperature favors the exothermic direction, decreasing K.

Equilibrium Shifts and Ice Tables

• Changes in concentration due to stress can be calculated using an ICE table (Initial, Change, Equilibrium).
• The change (x) is calculated by plugging the new equilibrium concentrations into the equilibrium constant expression and solving for x.

Factors that Do Not Affect Equilibrium

• Catalysts: Catalysts speed up both forward and reverse reactions equally, not affecting equilibrium position.
• Adding Inert Gases: Adding an inert gas to a sealed container increases pressure, but it does not alter the concentrations of reactive components, thus no shift in equilibrium.