Le Châtelier’s Principle

Le Châtelier’s Principle If a stress is applied to a system at equilibrium, the system shifts in the direction that relieves the stress. Stress is anything that upsets equilibrium – concentration, pressure, or temperature.

Concentration Measure of molarity (moles/L) If you ↑concentration of a reactant, equilibrium will shift toward the products. If you ↓concentration of a reactant, equilibrium will shift toward the reactants.

CO(g) + 3H2(g) ↔ CH4(g) + H2O(g)

Pressure Ideal Gas Law: PV=nRT If ↑P then ↑n, which means more number of atoms. If ↑P, then the equilibrium will shift toward the side with fewer moles of gas.

CO(g) + 3H2(g) ↔ CH4(g) + H2O(g) 4 moles of gas 2 moles of gas Note: If moles of gaseous reactant = moles of gaseous product, then no shift in equilibrium will occur from a change in pressure

Think of heat as a reactant or a product. Temperature Think of heat as a reactant or a product. CO(g) + 3H2(g) ↔ CH4(g) + H2O(g) + heat Is this Exothermic or Endothermic?

CO(g) + 3H2(g) ↔ CH4(g) + H2O(g) + heat

Le Châtelier’s Principle If a stress is applied to a system at equilibrium, the system shifts in the direction that relieves the stress. Concentration Pressure Temperature Note: Only temperature affects K. The larger the value of K, the more product at equilibrium.