Thermodynamics of proton dissociation of acridinium ion in aqueous solution

Standard thermodynamic function changes (AGO”, AHe’, A&” and Acre”) are reported for proton dissociation of acridinium cation in aqueous solution. These values have been determined from a series of precise and accurate acid equilibrium constants, K,. The equilibrium constants have been obtained spectrophotometrically over a range of temperatures from 2 to 66°C at several ionic strengths (I = 0.005, 0.007, 0.01, 0.05 and 0.25 M). Although the ionic strength does not affect in general the Gibbs free-energy values, the results suggest a possible influence on entropy and enthalpy changes.