Thermodynamics of the H+/Na+ and H+/Cs+ exchange on tin(IV) antimonate in methanolic solution

Addition of methanol decreases Delta G degrees, Delta H degrees and Delta S degrees of the exchange of Na+ or Cs+ for H+ in tin(IV) antimonate. Thus, the increase of selectivity constant is due to the decrease in the enthalpy term. On going from 30 to 90% (w/w) methanol, negative enthalpy and entropy changes occur may be due to chemisorption of methanol. In the 30 and 60% (w/w) methanol solutions, both Delta H degrees and Delta S degrees are lower than in aqueous medium. Thus, the decrease of Delta G degrees on addition of methanol is due to the enthalpy term. The Na+/H+ exchange reaction is entropy directed while the Cs+/H+ exchange is enthalpy directed.