Enthalpies of formation of low albite (NaAlSi₃O₈), gibbsite (Al(OH)₃), and NaAlO₂; revised values for ΔH°_f,298 and ΔG°_f,298 of some aluminosilicate mineral

The enthalpies of formation from the elements ΔH°_t, of low albite, analbite, NaAlSi₃O₈ glass, gibbsite (Al(OH)₃), and NaAlO₂, have been determined by hydrofluoric acid solution calorimetry from measurements of the heats of solution, ΔH°_soln, of low albite, NaAlO₂, SiO₂, Al(OH)₃, Al, H₂O, NaCl, and HC1-12.731H₂O in 20.1 weight percent HF(aq) at temperatures between 303.15 and 348.15 K. At 298.15 K the enthalpies of formation, ΔH°_f,298, for low albite, analbite, NaAlSi₃O₈ glass, gibbsite (Al(OH)₃), and NaAlO₂ are -3 935 115±3415, -3 924 235±3640, -3 875 455±3700, ±1293130±1190, and 1135 990±1255 J mol^-1, respectively. Our values for the enthalpies of formation of low albite, analbite, and for NaAlSi₃O₈ glass are approximately 13 810 J mol^-1 more negative than the values calculated by D. R. Waldbaum in 1968. Our value for the enthalpy of formation of gibbsite at 298.15 K is 11234 J more negative than the value of R. Barany and K. K. Kelley obtained in 1961. The standard Gibbs free energies of formation, ΔG°_f,298 for low albite, analbite, and gibbsite calculated from the above enthalpies and the appropriate entropy data are -3 711 715±3435, -3 706 500±3660, and -1154 890±1200 J mol^-1, respectively. The enthalpy of solution of Standard Reference Material 1654, α-quartz (37 to 74 μm), in 20.1 wt percent HF(aq) is -137 737±209 J mol^-1 at 333.15 K. This value is approximately 1255 J less negative than the value obtained by King in 1951 and 1952 for material that has a mean particle diameter of less than 5 μm and that has been used by the U.S. Bureau of Mines in their determinations of the enthalpies of formation of many silicates. Revised values of the enthalpies and Gibbs free energies of formation are presented for some aluminosilicate minerals, based upon this new data for ΔH°_f,298 of gibbsite and the heat of solution of α-quartz.