Keq as a pivotal concept in chemical equilibrium

The equilibrium constant (Keq) quantifies the ratio of product concentrations to reactant concentrations for a reversible reaction at equilibrium

Keq as a fixed ratio

Comparison to the number of players on a sports team during a game

Keq is similar to the number of players on a sports team, representing the balance between the forward and reverse reactions

Keq as a predictor of reaction direction and extent

Keq is instrumental in predicting the direction and extent of a reaction based on the concentrations of chemical species at equilibrium

Keq as a dimensionless value

Keq is a dimensionless value that provides a snapshot of the relative concentrations of reactants and products at equilibrium for a particular reaction at a constant temperature

Expression of Keq in terms of molar concentrations or partial pressures

Kc for reactions involving aqueous or gaseous species

Keq can be expressed in terms of molar concentrations (Kc) for reactions involving aqueous or gaseous species

Kp for reactions involving gases

Keq can be expressed in terms of partial pressures (Kp) for reactions involving gases

Derivation of Keq expressions from balanced chemical equations

The expressions for Kc and Kp are derived from the coefficients of the balanced chemical equation, where the concentrations or partial pressures of the products and reactants are raised to the power of their respective stoichiometric coefficients

Calculation of equilibrium concentrations or partial pressures

The equilibrium constant is calculated by determining the equilibrium concentrations or partial pressures of the reactants and products, which can be estimated from the initial concentrations and the stoichiometry of the balanced chemical equation

Homogeneous equilibria

In homogeneous equilibria, all reactants and products are in the same phase, and their concentrations or partial pressures contribute to the equilibrium constant expression

Heterogeneous equilibria

In heterogeneous equilibria, the concentrations of pure solids and liquids are excluded from the equilibrium constant expression because their concentrations are constant and do not affect the equilibrium position

Procedural steps for calculating Keq using known or deduced equilibrium concentrations

The calculation of the equilibrium constant involves setting up an ICE (Initial, Change, Equilibrium) table and applying stoichiometric relationships to determine the equilibrium concentrations or partial pressures

Calculation of Keq from thermodynamic data

The relationship between Keq and the standard Gibbs free energy change (ΔG°) can be described by the equation ΔG° = -RT ln(Keq)

Inference of Keq from standard electrode potentials

Keq can be inferred from the standard electrode potentials (E°) of electrochemical reactions using the Nernst equation, E° = (RT/nF) ln(Keq)

Alternative methods for determining Keq when direct equilibrium measurements are challenging

Thermodynamic approaches offer alternative methods for determining Keq, particularly when direct equilibrium measurements are challenging to obtain