Effect of Iodide Ion Concentration on the Equilibrium Position of the Iodine Reaction

Abstract

Chemical equilibrium is a reversible condition in which the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. This dynamic state, represented by a bidirectional arrow (⇌), continues at the molecular level without observable macroscopic changes. According to Le Chatelier’s principle, any change in concentration, temperature, pressure, or volume causes the equilibrium to shift in a direction that counteracts the disturbance. The equilibrium constant (K) quantitatively expresses the ratio of product and reactant concentrations at equilibrium, indicating the reaction’s extent. This study aimed to determine the equilibrium constant (Kc) for the reaction I₂ + I⁻ ↔ I₃⁻ through solvent distribution and iodometric titration methods. The experiment investigated how varying KI concentrations affect iodine solubility and triiodide ion formation. Results revealed that higher KI concentrations increased iodine solubility, favoring I₃⁻ formation and shifting the equilibrium toward the products. The equilibrium constant (Kc) at 30°C was calculated to be 48, indicating a strong tendency for triiodide ion formation under the given conditions. These findings demonstrate that iodide ion concentration plays a crucial role in determining iodine solubility and the equilibrium position of the reaction system.