Determination and Validation of Standard Enthalpies of Formation and Sublimation of Potassium Salts Using Solution Calorimetry and Quantum‐Chemical Calculations

This work aims to develop an approach for the systematic determination of the formation and sublimation enthalpies of inorganic compounds using the examples of potassium bicarbonate, potassium carbonate, and potassium formate. The standard enthalpies of formation in the solid and gas phases are determined using solution calorimetry and the G4 method, respectively, while the enthalpies of sublimation are calculated from lattice energies. Density functional theory (DFT) calculations at the PBE-D3/projector-augmented-wave level are well-suited to determine sublimation enthalpies based on lattice energies and thus to validate the standard enthalpies of formation of inorganic compounds in the solid and gas phases. The uncertainty associated with the determination of standard formation enthalpies in the solid phase using solution calorimetry is roughly 0.5 kJ·mol^-1, while the uncertainty of sublimation enthalpies from DFT calculations is approximately less than 10 kJ·mol^-1, consistent with recent benchmark studies on representative molecular test sets. Given that the determination of sublimation enthalpies for salts based on vapor pressures is currently not feasible with existing techniques, DFT calculations are a promising approach for determining this quantity. In conclusion, the combination of solution calorimetry and quantum-chemical calculations offers a consistent framework for determining key thermodynamic properties of inorganic salts.