How is Keq related to molality?

Question

Avery Adams · Accepted Answer

Depending on the reference state used to calculate the value of Keq, the concentrations of reactants and products included in equilibrium constants (Keq) can be expressed in terms of molality or molarity. The value of Keq can be calculated from the equation
#K_(eq)=exp((-DeltaG^0)/(RT))#
where #DeltaG^0# is the standard change in Gibbs Free Energy of the reaction under standard conditions.  Standard conditions can be chosen as molarity (with a reference state of 1M) or molality (with a reference state of 1m), and the numerical value of Keq will be different depending on which reference state is chosen. In this case, there is no practical difference between the values of Keq for these two different choices of reference state because the difference between molarity and molality for dilute aqueous solutions at room temperature is very small. However, for the most accurate work, it is necessary to determine which reference state was used in the calculation of Keq and use those units, respectively. Since the values of Keq for the various reference states will be important for nonaqueous solutions, knowing how Keq was calculated is crucial in this situation.

Avery Adams · Answer

undefined Keq, the equilibrium constant, is related to molality through the concentration of solutes in a solution. Keq is determined using concentrations, which can be expressed in molality for solutions where the solvent is water. The relationship between Keq and molality can be expressed using the equation: Keq = [products]^m / [reactants]^n, where m and n are the stoichiometric coefficients and the concentrations are expressed in molality.