Thermochemical data for merlinoite; 1, Low-temperature heat capacities, entropies, and enthalpies of formation at 298.15 K of six synthetic samples having various Si/Al and Na/(Na + K) ratios Available to Purchase

The heat capacities, C_P, and heats of solution, ΔH_soln, of six synthetic merlinoite samples having various Si/Al and Na/(Na + K) ratios were measured by low-temperature, adiabatic calorimetry and hydrofluoric acid solution calorimetry, respectively. Merlinoite heat capacities were measured from 10 to 320 K, and enthalpies of formation from the elements, ΔH°_f, were determined from measurements of the heats of solution of Si0₂ (α-quartz), Al(OH)₃ (gibbsite), NaF, KF, and the merlinoite samples in 24.4 wt% HF_(aq) at 35 °C and 50 °C. The heat capacities of these samples show one large and two smaller glass-type transitions attributed to changes in the entropic state of the zeolitic water molecules.

Tables of the thermodynamic functions $CP0,ST0−S00,(HT0−H00)/T$⁠, and $−(GT0−H00)/T$ are presented for these six samples from 5 to 310 K. Configurational entropy contributions to the third-law entropies resulting from mixing on exchangeable cation, tetrahedral, and water sites were estimated. The configurational entropy contribution was estimated to be about 17% of the calorimetrically determined value of $S2980−S00$⁠. The following values for $ST0$ and $ΔHf,2980$ at 298.15 K (25 °C) were obtained: