Notes on Chemical Equilibrium

Key Concepts of Chemical Equilibrium

• Irreversible Reactions

  • Reactions that proceed in one direction, e.g., neutralization of NaOH and HCl:
  • NaOH + HCl → NaCl + H2O

• Reversible Reactions

  • Products can convert back to reactants.
  • Rate of forward reaction equals rate of backward reaction at equilibrium.

• Chemical Equilibrium

  • Observed in biological systems and industrial processes.
  • Focus on yield (amount of product) rather than reaction speed (kinetics).

• Factors Affecting Equilibrium

  • Temperature, pressure, and catalysts are manipulated to optimize yield.

• Equilibrium Constant (Kc)

  • Reflects the ratio of concentration of products to reactants at equilibrium:
  • For reaction aA + bB ⇌ cC + dD:
  • Kc = [C]^c [D]^d / [A]^a [B]^b

• Le Chatelier’s Principle

  • A system at equilibrium will respond to changes (concentration, temperature, pressure) to counteract the change.

• Reaction Quotient (Q)

  • Q compares concentrations at any point in time to Kc:
  • Q < Kc: Forward reaction favors products.
  • Q = Kc: System is at equilibrium.
  • Q > Kc: Reverse reaction favors reactants.

• Homogeneous vs Heterogeneous Equilibrium

  • Homogeneous: All substances in the same phase.
  • Heterogeneous: Substances in different phases (e.g., solid, liquid, gas).

• Entropy and Enthalpy at Equilibrium

  • At equilibrium, Gibbs free energy change (∆G) = 0.
  • Balance between entropy (disorder) and enthalpy (energy).

• Calculating Kp

  • For reactions involving gases, expressed in terms of partial pressures:
  • Kp = (P^2NO2) / (P^N2O4)

• Dynamic Nature of Equilibrium

  • Continuous interchange between reactants and products, no observable change in concentrations.