Equilibrium Constants

Definition

Equilibrium constants are numerical values that express the ratio of the concentrations of products to the concentrations of reactants at equilibrium for a given chemical reaction. These constants provide insight into the extent to which a reaction favors the formation of products or reactants under specific conditions, and they can vary with changes in temperature and pressure.

5 Must Know Facts For Your Next Test

1. The equilibrium constant, represented as K, is calculated using the formula $$K = \frac{[products]}{[reactants]}$$, where concentrations are raised to the power of their coefficients from the balanced equation.
2. If K > 1, the reaction favors the formation of products; if K < 1, the reaction favors reactants.
3. Equilibrium constants are temperature dependent, meaning a change in temperature will alter the value of K for a reaction.
4. For reactions involving solids and liquids, their concentrations do not appear in the expression for K since their activities are considered constant.
5. The equilibrium constant can also be expressed in terms of partial pressures for gas-phase reactions, using $$K_p$$ instead of $$K_c$$.

Review Questions

• How does changing temperature affect the equilibrium constant for a given reaction?
  • Changing the temperature impacts the equilibrium constant because it alters the energy dynamics of the reaction. For exothermic reactions, increasing temperature typically decreases K, favoring reactants. Conversely, for endothermic reactions, increasing temperature increases K, favoring products. This relationship is essential to understanding how shifts in conditions influence chemical equilibria.
• Compare and contrast dynamic equilibrium and static equilibrium in terms of chemical reactions and their corresponding equilibrium constants.
  • Dynamic equilibrium involves continuous movement where both forward and reverse reactions occur at equal rates, maintaining constant concentrations of reactants and products. In contrast, static equilibrium occurs when there is no movement or change; hence no equilibrium constant applies. The concept of dynamic equilibrium is crucial since it allows for calculating an equilibrium constant (K) that reflects how far a reaction has progressed toward products or reactants.
• Evaluate how Le Chatelier's Principle applies to changes in concentration and pressure within a system at equilibrium, considering its impact on the equilibrium constant.
  • Le Chatelier's Principle states that a system at equilibrium will shift in response to changes in concentration or pressure to counteract disturbances. When concentration is increased for either reactants or products, the system shifts towards the side that consumes that substance. Similarly, increasing pressure will favor the side with fewer moles of gas. However, it's important to note that these shifts do not change the value of the equilibrium constant itself; rather, they just shift the position of equilibrium until a new balance is achieved at a constant K.

Related terms

Dynamic Equilibrium: A state in which the forward and reverse reactions occur at equal rates, 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 to counteract that change and restore a new equilibrium.

Gibbs Free Energy: A thermodynamic potential that indicates the spontaneity of a reaction; it is related to the equilibrium constant through the equation $$ ext{Δ}G = -RT ext{ln}(K)$$.