The ionization enthalpies of m-Cl, p-Cl and p-F benzoic acids were measured by LKB-2277 Bioactivity Monitor at 25℃ in water-ethanol mixtures. In the same solution, the corresponding ionization entropies were calculated. The substituted constants α were calculated according to Hammett equation, the corresponding enthalpic constants, entropic constants and entropic reaction constants were also calculated. The effects caused by solvent and substituent were explained by the interaction between solute and solvent, and by the above constants.

Key words: ETHANOL, WATER, BENZENECARBOXYLIC ACID P, IONIZATION, SOLVENT EFFECT, ENTROPY, ENTHALPY, SUBSTITUENT EFFECT