Equilibrium Constant (k)

Definition

The equilibrium constant (k) is a numerical value that expresses the ratio of the concentrations of products to reactants at equilibrium for a given chemical reaction. This value is temperature-dependent, meaning it can change with variations in temperature, and it provides insight into the extent of a reaction and whether it favors the formation of products or reactants. Understanding how temperature and pressure affect k is crucial for predicting the behavior of reactions in different conditions.

5 Must Know Facts For Your Next Test

1. The value of k can change with temperature; as temperature increases or decreases, the position of equilibrium shifts, affecting product and reactant concentrations.
2. For exothermic reactions, an increase in temperature generally results in a decrease in k, while for endothermic reactions, an increase in temperature results in an increase in k.
3. K is unitless, although it can be expressed in terms of concentration units based on the stoichiometry of the reaction.
4. The equilibrium constant only applies to reactions at equilibrium; if a system is not at equilibrium, k cannot be accurately determined.
5. Pressure changes can affect k for reactions involving gases; increasing pressure shifts the equilibrium toward the side with fewer moles of gas.

Review Questions

• How does Le Chatelier's Principle relate to changes in temperature and pressure on the equilibrium constant?
  • Le Chatelier's Principle explains that when a system at equilibrium experiences a change in temperature or pressure, the position of equilibrium shifts to counteract that change. For instance, if the temperature is raised in an exothermic reaction, the system will shift toward the reactants to lower the temperature, which can result in a decrease in the value of k. Similarly, changing pressure will favor the side of the reaction with fewer moles of gas, which also influences the concentration ratios reflected in k.
• Analyze how the equilibrium constant (k) can provide insights into whether a reaction favors products or reactants.
  • The equilibrium constant (k) quantitatively indicates the extent to which a reaction favors products or reactants at equilibrium. A large k value (greater than 1) suggests that products are favored at equilibrium, meaning that most of the reactants have converted to products. Conversely, a small k value (less than 1) implies that reactants are favored, indicating that only a small fraction of reactants have transformed into products. By analyzing k values under different conditions, one can predict how changes will shift the balance toward either side.
• Evaluate how understanding the factors affecting k can impact industrial processes and environmental chemistry.
  • Understanding how temperature and pressure affect the equilibrium constant (k) is crucial for optimizing industrial processes such as chemical manufacturing and environmental remediation. In industries, adjusting these factors can maximize product yields or minimize unwanted by-products by strategically shifting equilibria. For example, in ammonia synthesis via the Haber process, increasing pressure favors production due to fewer gas moles on the product side. Similarly, environmental chemists use this knowledge to understand pollutant behavior under varying conditions, enhancing strategies for contamination treatment and ecosystem management.

Related terms

Le Chatelier's Principle:

A principle stating that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change.

Reaction Quotient (Q): A measure of the relative amounts of products and reactants present during a reaction at any point in time, used to determine the direction in which a reaction will proceed to reach equilibrium.

Gibbs Free Energy (G): A thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure; it helps predict reaction spontaneity.