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 given chemical reaction at a specific temperature. This constant helps to predict the extent to which a reaction will proceed and the favorability of product formation, making it a crucial aspect of chemical reaction models.

5 Must Know Facts For Your Next Test

1. The equilibrium constant expression varies based on the balanced chemical equation; for example, for the reaction aA + bB ⇌ cC + dD, K is expressed as K = [C]^c[D]^d / [A]^a[B]^b.
2. K is temperature-dependent, meaning that changes in temperature can shift the position of equilibrium and alter the value of K.
3. If K > 1, products are favored at equilibrium; if K < 1, reactants are favored.
4. The equilibrium constant is dimensionless and can be calculated using molarity or partial pressures depending on the state of the reactants and products.
5. In heterogeneous equilibria involving solids or liquids, their concentrations do not appear in the equilibrium constant expression since they are considered to have a constant concentration.

Review Questions

• How does the equilibrium constant help in predicting the outcome of a chemical reaction?
  • The equilibrium constant provides a clear numerical representation of the ratio between products and reactants at equilibrium. By analyzing its value, one can determine whether a reaction favors product formation or if reactants are more prevalent. This predictive power is essential for understanding how changes in conditions, such as concentration or temperature, can influence the direction and extent of a reaction.
• Discuss how changes in temperature can affect the value of the equilibrium constant for an exothermic reaction.
  • For an exothermic reaction, increasing the temperature shifts the equilibrium position towards the reactants, thereby decreasing the value of the equilibrium constant. This occurs because heat acts as a reactant in exothermic processes. Conversely, lowering the temperature favors product formation, resulting in an increased K value. Thus, understanding this relationship is key when designing reactions under varying thermal conditions.
• Evaluate how Le Chatelier's Principle can be used alongside the equilibrium constant to predict shifts in chemical equilibria when external changes are applied.
  • Le Chatelier's Principle states that a system at equilibrium will adjust to counteract changes imposed upon it. When an external change occurs, such as altering concentration or pressure, this principle can be applied to predict how the system will respond. By analyzing the equilibrium constant before and after these changes, one can gauge whether products or reactants will be favored at the new equilibrium state, making it easier to understand complex reactions and their behavior under varying conditions.

Related terms

Chemical Equilibrium: A state in a chemical reaction where the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products.

Le Chatelier's Principle: A principle stating that if an external change is applied to a system at equilibrium, the system will adjust itself to counteract that change and restore a new equilibrium.

Reaction Quotient: A ratio that measures the relative concentrations of products and reactants at any point in a reaction, allowing comparison with the equilibrium constant to predict direction of reaction shift.