Equilibrium Constant

Definition

The equilibrium constant, denoted as K, is a numerical value that expresses the ratio of the concentrations of products to the concentrations of reactants at equilibrium for a reversible chemical reaction. It provides insight into the position of equilibrium and helps predict the extent to which a reaction will proceed, indicating whether products or reactants are favored under specific conditions.

5 Must Know Facts For Your Next Test

1. The equilibrium constant expression varies depending on the balanced chemical equation; it is derived from the law of mass action.
2. For a general reaction aA + bB ⇌ cC + dD, the equilibrium constant is defined as K = \frac{[C]^c[D]^d}{[A]^a[B]^b}.
3. If K > 1, products are favored at equilibrium, while if K < 1, reactants are favored, indicating how far the reaction proceeds towards completion.
4. Changes in temperature can affect the value of K; it is only constant at a specific temperature for a given reaction.
5. K can be expressed in terms of concentrations (Kc) or partial pressures (Kp), and there is a relationship between Kc and Kp based on the ideal gas law.

Review Questions

• How does the equilibrium constant relate to the concentrations of reactants and products in a chemical reaction?
  • The equilibrium constant quantitatively relates the concentrations of products and reactants when a reaction reaches equilibrium. For a balanced equation, K is calculated by taking the ratio of product concentrations raised to their stoichiometric coefficients over the reactant concentrations raised to their coefficients. This relationship allows for predicting whether a reaction will favor products or reactants based on the values of K.
• Discuss how changes in temperature impact the equilibrium constant for an exothermic reaction.
  • For an exothermic reaction, increasing temperature generally decreases the value of the equilibrium constant. This occurs because higher temperatures favor the endothermic direction of the reaction, shifting equilibrium towards reactants. Conversely, lowering temperature increases K, promoting product formation. Understanding this temperature dependence is crucial for controlling reactions in industrial processes.
• Evaluate the significance of the equilibrium constant in industrial applications and how it influences process design.
  • The equilibrium constant plays a critical role in industrial applications by guiding process design and optimization. By knowing K values, engineers can determine optimal conditions—like pressure, temperature, and concentration—to maximize product yield. Furthermore, understanding how changes in these conditions affect K allows for strategic adjustments in reactor design and operation, ultimately enhancing efficiency and profitability in chemical manufacturing.

Related terms

Le Chatelier's Principle: A principle stating that if a dynamic equilibrium is disturbed by changing the conditions, the system shifts in the direction that counteracts the change.

Reaction Quotient (Q): A measure similar to the equilibrium constant but calculated using the current concentrations of reactants and products, allowing for comparison to K to predict reaction direction.

Stoichiometry: The calculation of reactants and products in chemical reactions, which is essential for determining the relationships between quantities in balanced equations.