Abstract :
Calorimetric measurements have been performed on the melt–gas systems M2S2O7–V2O5 and M2S2O7–M2SO4(sat)–V2O5 (M=K and Cs) in SO2(g) and Ar(g) at 430–480°C and for mole fractions XV2O5=0–0.1. Enthalpies have been obtained for complex formation reactions as (VO)2O(SO4)44−+SO42−⇄2VO2(SO4)23−+S2O72− for V(V) and 2VO(SO4)22−+3SO42−+SO3⇄2VO(SO4)34−+S2O72− for V(IV). Similarly enthalpies of the V(V)–V(IV) redox reactions (VO)2O(SO4)44−+SO2⇄2VO(SO4)22−+SO3 and 2VO2(SO4)23−+SO42−+SO2⇄2VO(SO4)34− could be calculated. These enthalpies of reduction compare well with those obtained by spectrophotometric measurements in the same temperature range.
