The reaction between iodine I2 and thiosulfate S2O3^2- can be represented as follows:2 S2O3^2- aq + I2 aq S4O6^2- aq + 2 I^- aq To determine the equilibrium constant Kc for this reaction, we need to know the equilibrium concentrations of all species involved. Unfortunately, the equilibrium constant for this reaction is not a fixed value, as it depends on factors such as temperature and the specific conditions under which the reaction is carried out.However, in many cases, the reaction between iodine and thiosulfate is considered to be a fast and quantitative reaction, meaning that it proceeds to completion with very little equilibrium established. In these cases, the equilibrium constant would be very large, indicating that the reaction strongly favors the formation of products S4O6^2- and I^- over the reactants S2O3^2- and I2 .