Thermodynamic Data

In solutions, there are interactions between all possible species such as dissociated ions, ionpairs, molecules, etc, that interfere with the behavior of the solutes. According to thedefinition given by IUPAC, thermodynamic data always refer to a selected standard state.Considering this definition, at the standard state of pressure, the concentration (in molalscale) of a solute B in a solution and its activity coefficient should be both unities.Unfortunately, for many (or all) reactions, the situation cannot be made accurately and thesolution needs to be diluted and extrapolated to reach the standard state which is alwaysaccompanied with a large error. Precise thermodynamic information for these systems canonly be obtained in the presence of an inert electrolyte with sufficiently high concentration,ensuring that activity factors are reasonably constant throughout the measurements.