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. It provides insight into the extent of a reaction and helps predict the concentrations of substances when the system reaches equilibrium. The value of k is temperature-dependent and plays a crucial role in understanding how changes in conditions affect a reaction's position of equilibrium.

5 Must Know Facts For Your Next Test

1. The value of the equilibrium constant k is calculated using the formula $$k = \frac{[products]}{[reactants]}$$, where concentrations are raised to the power of their coefficients in the balanced equation.
2. If k >> 1, it indicates that at equilibrium, products are favored, while k << 1 suggests that reactants are favored.
3. The equilibrium constant is specific to a particular reaction at a given temperature; changing the temperature will change the value of k.
4. The units of k can vary depending on the reaction, but it is often dimensionless when using concentrations in molarity.
5. For reactions involving gases, the equilibrium constant can also be expressed in terms of partial pressures instead of concentrations.

Review Questions

• How does the value of the equilibrium constant k help predict whether products or reactants are favored at equilibrium?
  • The value of the equilibrium constant k provides direct insight into the extent of a reaction. If k is much greater than 1, it means that at equilibrium, there are significantly more products than reactants, indicating that the reaction favors product formation. Conversely, if k is much less than 1, reactants dominate at equilibrium, showing that the reaction does not proceed extensively towards product formation.
• Explain how Le Chatelier's Principle applies to changes in concentration and its effect on the equilibrium constant k.
  • Le Chatelier's Principle states that when a system at equilibrium experiences a change in concentration, pressure, or temperature, it will shift in such a way as to counteract that change. For instance, if the concentration of reactants is increased, the system will shift towards forming more products to restore equilibrium. However, it's important to note that while concentrations may change as a response to shifts, the actual value of the equilibrium constant k remains unchanged unless there is a temperature variation.
• Analyze how varying temperature affects the equilibrium constant k for an exothermic versus an endothermic reaction.
  • In exothermic reactions, where heat is released, increasing the temperature will shift the equilibrium position toward reactants and decrease the value of k. This happens because adding heat acts as a stress that favors reactant formation. In contrast, for endothermic reactions that absorb heat, raising the temperature shifts equilibrium toward products, resulting in an increased value of k. This reflects how changes in thermal energy influence reaction dynamics and favorability based on enthalpic contributions.

Related terms

Dynamic Equilibrium:

A state in which the rates of the forward and reverse reactions are equal, leading to constant concentrations of reactants and products.

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.

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