Equilibrium Constant

Definition

The equilibrium constant is a numerical value that expresses the ratio of the concentrations of products to the concentrations of reactants for a reversible chemical reaction at equilibrium. This constant provides insight into the position of equilibrium, indicating whether reactants or products are favored in a given reaction. A larger equilibrium constant signifies a greater concentration of products compared to reactants, while a smaller value suggests the opposite.

5 Must Know Facts For Your Next Test

1. The equilibrium constant (K) is temperature-dependent; changing the temperature will alter its value.
2. For a reaction represented as $$aA + bB \rightleftharpoons cC + dD$$, the equilibrium constant is expressed as $$K = \frac{[C]^c[D]^d}{[A]^a[B]^b}$$.
3. If K > 1, it indicates that at equilibrium, the products are favored over the reactants, whereas if K < 1, reactants are favored.
4. Equilibrium constants can differ for reactions based on their physical states, such as gases versus solids or liquids.
5. The units of K depend on the specific reaction and may be dimensionless or have units of concentration.

Review Questions

• How does the equilibrium constant help predict the direction of a reversible chemical reaction?
  • The equilibrium constant provides valuable information about the relative concentrations of products and reactants at equilibrium. By comparing the value of the reaction quotient (Q) to K, one can determine if a reaction will proceed forward or reverse to reach equilibrium. If Q < K, it indicates that more products need to form; if Q > K, then more reactants must be produced.
• Evaluate how changes in temperature affect the value of an equilibrium constant and provide an example.
  • Changes in temperature can significantly impact the value of an equilibrium constant because K is dependent on temperature. For instance, for an endothermic reaction, increasing temperature will shift the equilibrium toward the product side, resulting in a larger K value. Conversely, for an exothermic reaction, increasing temperature shifts equilibrium toward reactants, leading to a smaller K. This relationship highlights the dynamic nature of chemical equilibria.
• Synthesize information on how Le Chatelier's Principle relates to shifts in equilibrium when external stresses are applied and how this affects the equilibrium constant.
  • Le Chatelier's Principle states that when an external stress, such as a change in concentration, pressure, or temperature, is applied to a system at equilibrium, the system will adjust to counteract that stress. For example, if you increase the concentration of a reactant, the system will shift toward producing more products to restore equilibrium. However, while Le Chatelier's Principle explains how systems respond to changes, it is important to note that such adjustments do not alter the value of the equilibrium constant unless temperature changes; K remains constant for specific conditions even if concentrations shift.

Related terms

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 (Q): A ratio that describes the relative concentrations of products and reactants at any point in time during a reaction, used to predict the direction in which the reaction will proceed to reach equilibrium.

Dynamic Equilibrium: A state in which the rate of the forward reaction equals the rate of the reverse reaction, resulting in constant concentrations of reactants and products.