Chemistry Chapter 15: Chemical Equilibrium

Chapter 15: Chemical Equilibrium

• Chemical equilibrium occurs when the forward and reverse reaction rates are equal.
• A double arrow indicates a reversible reaction that is at equilibrium.
• Equilibrium expressions relate products and reactants at equilibrium.
• $K = \frac{[C]^{c}[D]^{d}}{[A]^{a}[B]^{b}}$ (Where K is the equilibrium constant, and a, b, c, and d are stoichiometric coefficients for the balanced reaction A + B ⇌ C + D).
• K > 1 favors the forward reaction (products).
• K < 1 favors the reverse reaction (reactants).
• K = 1 favors both forward and reverse equally.

Equilibrium Constants

• Equilibrium constants (K) are temperature-dependent.
• K represents a ratio of product to reactant concentrations at equilibrium.
• Kp is equilibrium expressed in terms of partial pressures.
• Kp = Kc(RT)^An (Where R is the ideal gas constant, T is the temperature in Kelvin, and An is the change in moles of gas).

Using Equilibrium Expressions

• Equilibrium expressions can determine equilibrium concentrations and pressures.
• ICE tables (initial, change, equilibrium) organize calculation of equilibrium values.
• Manipulating equilibrium reactions changes equilibrium values.
  • Reversing the reaction inverts the equilibrium constant.
  • Multiplying the coefficients by a factor raises the equilibrium constant to that power.
  • Adding reactions multiplies the equilibrium constants.
• The reaction quotient (Q) compares non-equilibrium concentrations or pressures to the equilibrium constant (K).
• Q < K favors product formation (shifts right).
• Q = K, the reaction is at equilibrium.
• Q > K favors reactant formation (shifts left).

Le Chatelier's Principle

• External factors (temp, pressure, and concentration) alter equilibrium.
• The system adjusts by counteracting the change to minimize shift from equilibrium.
• Concentration Changes:
  • Increased concentration of a reactant favors production of products (shifts right).
  • Decreased concentration of a reactant favors production of reactants (shifts left).
• Pressure Changes:
  • Increased pressure favors the side with fewer moles of gas (shifts left, fewest moles).
  • Decreased pressure favors the side with more moles of gas (shifts right, most moles).
• Temperature Changes:
  • Endothermic reactions favor products at higher temps (shifts right).
  • Exothermic reactions favor products at lower temps (shifts right).
• Catalysts: Catalysts speed up reactions by lowering activation energy of forward and reverse reaction, but they do not affect position of equilibrium.

Explore the principles of chemical equilibrium in this quiz. Understand the significance of equilibrium constants, K values, and how they relate to forward and reverse reactions. Test your knowledge on equilibrium expressions and their applications in chemical reactions.