Chapter 13: Equilibrium Concepts Summary

  • Chapter 13 Outline

    • 13.1 Chemical Equilibrium
    • 13.2 Equilibrium Constants
    • 13.3 Shifting Equilibria: Le Châtelier’s Principle
    • 13.4 Equilibrium Calculations

  • Dynamic Equilibrium

    • Single arrow: complete reaction;
    • Double arrow: partial conversion (dynamic process).
    • Example: Reaction of nitrogen tetroxide ($N2O4$) to nitrogen dioxide ($NO_2$) is dynamic at equilibrium.

  • Chemical Equilibria

    • Equilibrium reached when forward and reverse reaction rates are equal.
    • Color change from $N2O4$ to $NO_2$ observed.

  • Common Misconceptions

    • Amounts of reactants/products aren't equal at equilibrium;
    • Equilibrium is dynamic, not static.

  • Establishment of Equilibrium

    • Forward reaction rate decreases as $N2O4$ concentration increases, reverse increases as $NO_2$ accumulates.

  • Equilibrium Constants

    • Reaction quotient (Q) indicates system state; $K$ is constant at equilibrium.
    • Form: $K= rac{[C]^c[D]^d}{[A]^a[B]^b}$

  • Comparing Q and K

    • $Q < K$: system shifts forward;
    • $Q > K$: shifts backward;
    • $Q = K$: at equilibrium.

  • Heterogeneous vs. Homogeneous Equilibria

    • Homogeneous: all species in same phase (gas/liquid);
    • Heterogeneous: species in different phases; solids/liquids excluded from equilibrium expressions.

  • Le Châtelier’s Principle

    • System at equilibrium shifts to minimize disturbances (concentration, temperature, pressure).

  • Influences on Equilibrium

    • Adding/removing reactants/products shifts system accordingly.
    • Temperature changes affect $K$:
    • Exothermic: $K$ decreases with increase in T.
    • Endothermic: $K$ increases with increase in T.
    • Pressure changes influence equilibrium based on moles of gas.

  • Equilibrium Calculations

    • Determine changes in concentrations/pressures; calculate equilibrium states using initial values.
    • Example calculation: $ ext{Initial concentration} + ext{Change} = ext{Equilibrium concentration}$.

  • Practice Problems

    • Work on the practice problems in ACS Preparation Book as assigned (SQ and PQ numbers).