Equilibrium Concentrations

Equilibrium Constant

Keq = [products] / [reactants]

• Keq > 1 → Products favored at equilibrium.

• Keq < 1 → Reactants favored at equilibrium.

• Keq ≈ 1 → Significant amounts of both reactants & products present.

Reaction Quotient vs Equilibrium Constant

• Q = [products] / [reactants]

• Q is calculated the same way as Keq, but it uses initial concentrations instead of equilibrium concentrations.

• Q < Keq → Reaction shifts right (toward products).

• Q > Keq​ → Reaction shifts left (toward reactants)

• Q = Keq​ → System is at equilibrium.

Le Châtelier’s Principle

If a system at equilibrium is disturbed, it will shift in a direction that counteracts the disturbance.

Shifts RIGHT

• Concentration Changes

  • Add reactant

  • Remove product

• Temperature Changes

  • Exothermic Rxn: Decrease temp

  • Endothermic Rxn: Increase temp

Shifts LEFT

• Concentration Changes

  • Remove reactant

  • Add product

• Temperature Changes

  • Exothermic Rxn: Increase temp

  • Endothermic Rxn: Decrease temp

Q < Kc

• Too little products

Reactants = Consumed

Products = Produced

Q = Kc

• Equilibrium

  Reactants = No Change

  Products = No Change

Q > Kc

• Too much products

  Reactants = Produced

  Products = Consumed