Composition of vapor and thermodynamic characteristics of gaseous molecules tungstates of alkali earth metals

Calculated and experimental mass spectra (at temperatures region of 1600 – 2000 K) of gaseous alkaline earth metals tungstates: MgWO4(g), CaWO4(g), SrWO4(g), BaWO4(g) are given. The partial vapor pressures are determined and the equations for the temperature dependences of the partial pressures of gaseous molecules of alkaline earth metals tungstates were derived for liquid in the form (Р, atm): lgP(MgWO4(L)) = –28737/Т + 7,95 for the area 1600 – 1900 K; lgP(CaWO4(L)) = – 25265/Т + 6,913 for the area 1850 – 2000 K; lgP(SrWO4(L)) = – 25052/Т + 7,13 for the area 1800 – 1900 K; lgP(BaWO4(L)) = –20570/Т + 4,58 for the area 1770 – 1900 K. Based on experimental data on vapor pressure, the enthalpies of evaporation (DН0s,0), formation (–DН0f,0) and atomization (DН0at,0) of gaseous alkaline earth metals tungstates were calculated, which respectively amounted to (DН0, kJ/mol): MgWO4 — 652, 890, 2855; CaWO4 — 644, 974, 2968; SrWO4 — 615, 1045, 3056; BaWO4 — 548, 1045, 3095. The enthalpy of sublimation of alkaline earth metals tungstates decreases from magnesium to barium.