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 for a reversible chemical reaction at equilibrium. This constant provides insight into the extent of a reaction and is closely related to the chemical potential and Gibbs energy, indicating how far a reaction has proceeded towards completion.

5 Must Know Facts For Your Next Test

1. The equilibrium constant is temperature-dependent, meaning its value changes with variations in temperature, impacting how much product and reactant are present at equilibrium.
2. A large equilibrium constant (K >> 1) indicates that products are favored at equilibrium, while a small equilibrium constant (K << 1) suggests that reactants are favored.
3. The equilibrium constant is derived from the standard Gibbs free energy change ( abla G^ ext{o}) for the reaction, where K = e^(- abla G^ ext{o}/RT).
4. In reactions involving gases, the equilibrium constant can also be expressed in terms of partial pressures rather than concentrations, known as Kp.
5. Changing conditions such as concentration or temperature can shift the position of equilibrium according to Le Chatelier's principle, which does not affect the value of K at a given temperature.

Review Questions

• How does the equilibrium constant relate to Gibbs free energy and what does it indicate about a reaction?
  • The equilibrium constant is directly related to Gibbs free energy through the equation K = e^(- abla G^ ext{o}/RT). A negative Gibbs free energy change indicates that a reaction is spontaneous and will favor product formation, which corresponds to a large value of K. Therefore, the magnitude of K provides insight into how far a reaction proceeds toward products versus reactants at equilibrium.
• Discuss how changes in temperature can affect the value of the equilibrium constant for a given reaction.
  • The value of the equilibrium constant is influenced by temperature because it is derived from the standard Gibbs free energy change, which varies with temperature. According to van 't Hoff's equation, if a reaction is exothermic, increasing the temperature will decrease K, favoring reactants. Conversely, for an endothermic reaction, raising the temperature increases K, favoring products. This relationship emphasizes that K is not static but dynamic with respect to thermal conditions.
• Evaluate how Le Chatelier's principle explains shifts in equilibrium and impacts the interpretation of the equilibrium constant.
  • Le Chatelier's principle states that if an external change is applied to a system at equilibrium, the system will adjust to counteract that change. This principle helps explain how concentrations or pressures can shift to re-establish equilibrium without altering the actual value of the equilibrium constant at a fixed temperature. For example, adding more reactant will shift the balance towards products until a new equilibrium is reached, but K remains unchanged under these new conditions. This principle enhances our understanding of chemical systems by illustrating their adaptability while maintaining fundamental constants.

Related terms

Gibbs free energy: A thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure.

Reaction quotient: A ratio that compares the concentrations of products and reactants at any point in a reaction, not just at equilibrium, used to determine the direction of the reaction.

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.