Состав пара и термодинамические характеристики газообразных молекул молибдатов щелочных металлов

Abstract

Calculated and experimental mass spectra (at temperatures region of 1050 – 1800 K) of gaseous alkali metals molybdates: Li2MoO4, Na2MoO4, K2MoO4, Rb2MoO4, Cs2MoO4 are presented. The partial vapor pressures are determined and the equations for the temperature dependences of the partial pressures of gaseous molecules of alkali metal molybdates were derived in the form (Р, atm.): for liquid lgP(Li2MoO4(L)) = –14563/Т + 4,696 — for the area 1403 – 1504 K; for liquid lgP(Na2MoO4(L)) = =–13794/Т + 6,19 — for the area 1050 – 1300 K; for solid lgP(K2MoO4(S)) = –15206/Т + 7,09 — for the area 1170 – 1310 K; for solid lgP(Rb2MoO4(S)) = –17358/Т + 8,81 — for the area 1102 – 1208 K; for liquid lgP(Rb2MoO4(L)) = –16604/Т + 8,29 — for the area 1204 – 1307 K; for solid lgP(Cs2MoO4(S)) = –13724/Т + 6,47 — for the area 1026 – 1148 K. Based on experimental data on vapor pressure, the enthalpies of evaporation (∆H0s,0), formation (–∆H0f,0) and atomization (∆H0at,0) of gaseous alkali metals molybdates were calculated, which respectively amounted to (∆Н, kJ/mol): Li2MoO4 (406; 1012; 2970), Na2MoO4 (352; 1102; 2960), K2MoO4 ( 341; 1149; 2972), Rb2MoO4 (328; 1079; 2837), Cs2MoO4 (309; 1097; 2991). The enthalpy of sublimation of alkali metals molybdates decreases from lithium to cesium.