Final answer:
The concentration of reactants and products must be considered when calculating the equilibrium constant for aqueous solutes, as these concentrations influence the value of Keq.
Step-by-step explanation:
When calculating the equilibrium constant for aqueous solutes, it is important to consider the concentration of reactants and products. Unlike the pressure, volume of the container, or presence of a catalyst, the concentration of the solutes is a key variable that must be known to determine the equilibrium condition. For reactions occurring in solutions, solvent concentration is generally omitted from the equilibrium constant expression because it is in large excess and remains nearly constant.
To find the equilibrium constant (Keq), you would use the equilibrium concentrations (or partial pressures for gases) of the reactants and products. These are placed into the equilibrium expression, with products in the numerator and reactants in the denominator, and raised to the power of their stoichiometric coefficients. Solid and liquid phases, being pure substances, are represented as having an activity of 1 and do not appear in the expression.
Therefore, to answer the query, when calculating equilibrium constants, the factor to consider for aqueous solutes is the concentration of reactants and products. This is because during a reaction, their concentrations can change and they directly affect the value of the equilibrium constant.