Explaining activity coefficients and standard states in the undergraduate physical chemistry course

Abstract

The activity coefficient concept is one of the most difficult for students in the undergraduate physical chemistry course to grasp.

Systematic Approach for Calculating the Concentrations of Chemical Species in Multiequilibrium Problems: Inclusion of the Ionic Strength Effects

“…Because of ionic interactions, equilibrium constants may not be validly calculated using concentrations instead of activities. The concentrations are related to activities by false[ normalA i false] = a A i f A i where [A i ] is the molar concentration, a A i the corresponding activity, and f A i the factor that relates both parameters, called the activity coefficient. − Several equations have been suggested to calculate the activity coefficients. − The most successful equations use the ionic strength to quantify the effects of electrostatic interactions. Some empirical approximations to the Debye–Hückel equation are widely used. − The following expressions have been applied in this work to take into account the effect of the ionic strength on chemical equilibria, log nobreak0em.25em⁡ f i = prefix− 0.509 z i 2 ( I 1 + I − 0.1 I ) log nobreak0em.25em⁡ f i = prefix− 0.509 z i 2 ( I 1 + 1.5 I ) where z i is the ion charge and I is the ionic strength defined as I = …”