Equilibrium Constant

Definition

The equilibrium constant (K) is a numerical value that describes the ratio of the concentrations of products to reactants at equilibrium for a reversible chemical reaction at a given temperature. This constant provides insights into the extent of a reaction and indicates whether the reactants or products are favored under equilibrium conditions.

5 Must Know Facts For Your Next Test

1. The equilibrium constant is temperature-dependent; changing the temperature will alter its value.
2. For a general reaction of the form: $$aA + bB \rightleftharpoons cC + dD$$, the equilibrium constant is expressed as $$K = \frac{[C]^c[D]^d}{[A]^a[B]^b}$$.
3. If K > 1, products are favored at equilibrium; if K < 1, reactants are favored.
4. The units of K depend on the specific reaction and can be dimensionless, but often have units based on the stoichiometry of the balanced equation.
5. Changes in concentration or pressure will shift the position of equilibrium according to Le Chatelier's Principle, which can indirectly influence K.

Review Questions

• How does changing temperature affect the equilibrium constant of a given reaction?
  • Changing temperature affects the equilibrium constant because it alters the energy dynamics of the reaction. For exothermic reactions, increasing temperature typically decreases K, shifting the equilibrium toward reactants. Conversely, for endothermic reactions, increasing temperature raises K, favoring product formation. This temperature dependence highlights how heat can influence chemical equilibria.
• Discuss how the equilibrium constant relates to Gibbs free energy and spontaneity of reactions.
  • The relationship between the equilibrium constant and Gibbs free energy is crucial in understanding reaction spontaneity. The standard Gibbs free energy change (ΔG°) is related to K through the equation: $$\Delta G° = -RT \ln(K)$$. If K > 1, ΔG° is negative, indicating that the reaction is spontaneous in the forward direction. Conversely, if K < 1, ΔG° is positive, suggesting that reactants are favored and the reaction is non-spontaneous.
• Evaluate how Le Chatelier's Principle can be applied to predict changes in equilibrium when external conditions are altered.
  • Le Chatelier's Principle allows us to predict how a system at equilibrium responds to external changes such as concentration, pressure, or temperature shifts. For instance, if the concentration of a reactant is increased, the system will shift towards products to re-establish equilibrium. Similarly, if pressure increases in a gaseous reaction with unequal moles of gases on either side, it will shift toward the side with fewer moles. This predictive power aids in understanding dynamic equilibria and optimizing conditions for desired outcomes in biochemical processes.

Related terms

Le Chatelier's Principle: A principle stating that if a system at equilibrium is subjected to a change in concentration, temperature, or pressure, the system will adjust to counteract that change and restore a new equilibrium.

Gibbs Free Energy: A thermodynamic potential that measures the maximum reversible work obtainable from a system at constant temperature and pressure, related to the spontaneity of a reaction.

Reaction Quotient (Q): A ratio that compares the current concentrations of reactants and products during a reaction to determine the direction in which the reaction will proceed to reach equilibrium.