CHEM1010 W1 L1

Introduction to Chemical Equilibria

• Importance of contact details provided in lecture slides.

• Reference to an online textbook for access to graphs and tables.

• Analogy of precariously balanced stones to illustrate the concept of equilibrium being sensitive to changes.

Key Concepts

Reversibility of Reactions

• Irreversible Reactions:

  • Example: Baking a cake, where reactants cannot be recovered once mixed.

  • Example: A pine forest during a bushfire, where the original state cannot be regained.

Reversible Reactions

• General scheme: A + B ⇄ C + D

• Equilibrium Arrow: Indicates the reaction can proceed in both forward and reverse directions.

  • Both reactants and products coexist at equilibrium.

  • Dynamic equilibrium: concentrations of reactants and products remain constant over time despite ongoing reactions.

Dynamic Equilibrium

• Analogy of a person running on an escalator: no net movement observed, but processes are occurring.

• Equilibrium State:

  • Forward and reverse reactions occur at equal rates.

  • Concentrations of reactants and products appear unchanging.

Example of Dynamic Equilibrium

• Reaction of N₂O₄ and NO₂:

  • Reaction changes color as it reaches equilibrium between colorless N₂O₄ and brown NO₂.

  • Rates of formation and decomposition reach a balance, indicating equilibrium.

  • Color indicates concentration changes, leading to a visual cue for equilibrium.

Equilibrium Constants (K)

• Definition: Ratio of concentrations of products to reactants at equilibrium.

• Formulation:

  • K = [C]^c [D]^d / [A]^a [B]^b

  • Concentrations in square brackets; coefficients raised to powers of their respective compounds.

• Common equilibrium constants:

  • Kc: concentration-based constant

  • Kp: based on partial pressures for gas reactions

  • Ksp: solubility product constant for sparingly soluble salts

Factors Affecting Equilibrium Constants

• Only gases and ions in solution are considered; solids and liquids are excluded.

• The constant (K) is not assigned units and typically cancels out.

Equilibrium Position

• K value can indicate whether reactants or products are favored:

  • K > 1: Reaction favors products (more products than reactants).

  • K < 1: Reaction favors reactants (more reactants than products).

Exercises and Application

• Practical Calculation of K:

  • Engage with example problems of calculating and interpreting equilibrium constants.

• Haber Process:

  • A significant reversible reaction in ammonia production, utilized in fertilizer manufacturing.

  • Importance of understanding equilibrium to optimize industrial processes.

Conclusion

• Recognizing the significance of equilibrium in chemical reactions enhances understanding of reaction dynamics.

• Future discussions will focus on acid-base chemistry and the factors that influence equilibrium positions.