Thermodynamics of the [formula omitted] and [formula omitted] exchange on tin(IV) antimonate in methanolic solution

Abstract

Addition of methanol decreases δG°, δH° and δS° 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 δH° and δS° are lower than in aqueous medium. Thus, the decrease of δG° 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.