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Calculating Equilibrium Concentrations

Calculating equilibrium concentrations involves determining the amounts of reactants and products present when a reaction reaches dynamic equilibrium.

Key Concepts​

  • Dynamic Equilibrium: Forward and reverse reaction rates are equal
  • Equilibrium Constant (K): Ratio of product concentrations to reactant concentrations, each raised to their stoichiometric coefficients

General Form​

For aA + bB ⇌ cC + dD
K = [C]^c [D]^d / [A]^a [B]^b

Steps to Calculate Equilibrium Concentrations​

  1. Write the balanced chemical equation
  2. Define initial concentrations
  3. Set up an ICE table (Initial, Change, Equilibrium)
  4. Express equilibrium concentrations in terms of unknowns
  5. Solve using the equilibrium constant expression

Example​

For N₂ + 3 H₂ ⇌ 2 NH₃, with K and initial concentrations known:

  • Use ICE table to express [NH₃] at equilibrium
  • Solve the quadratic equation if necessary

Importance​

  • Predicts composition of a reaction mixture at equilibrium
  • Essential in chemical engineering, reaction optimization, and laboratory calculations
  • Helps understand reaction behavior under different conditions

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