Mass Spectrometric Studies at High Temperatures: XXIX, Thermal Decomposition and Sublimation of Alkali Metal Sulfates

Mass spectrometric investigations of the high temperature equilibrium vapor species over the solids Li 2 SO 4 , Na 2 SO 4 , K 2 SO 4 , Rb 2 SO 4 , and Cs 2 SO 4 have shown that the products of thermal decomposition are M(g), where M = Li, Na, K, Rb, or Cs, SO 2 (g), and O 2 (g). In addition, molecules like K 2 SO 4 (g), Rb 2 SO 4 (g), and Cs 2 SO 4 (g) were observed, and the results show that sublimation as molecules becomes increasingly important for the heavier alkali metal sulfates. The equilibrium constants at several temperatures and heats for the decomposition reaction image were determined for Li 2 SO 4 , Na 2 SO 4 , and K 2 SO 4 . Calculated values of the heats of decomposition for Na 2 SO 4 and K 2 SO 4 , for which thermodynamic data are available, were in agreement with the measured quantities. The heats and entropies of sublimation to monomeric molecules for K 2 SO 4 (s), Rb 2 SO 4 (s), and Cs 2 SO 4 (s) were ΔH 0 2 , 1154°K = 72.8 ± 2.0 kcal mole ‐1 and ΔS 0 S 1554°K = 29.2 ± 1.8 eu; ΔH 0 S , 1123°K = 69.7 ± 1.0 kcal mole ‐1 and ΔS 0 S, 1123°K = 27.4 ± 0.8 eu; and ΔH 0 S, 1081°K = 63.9 ± 1.7 kcal mole ‐1 and ΔS 0 S, 1081°K = 26.2 ± 1.6 eu, respectively.