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

## TL;DR

The paper presents a method combining solution calorimetry and quantum calculations to determine thermodynamic properties of potassium salts.

## Contribution

A new framework combining experimental and computational methods to determine formation and sublimation enthalpies of inorganic salts.

## Key findings

- Solution calorimetry and G4 method determine solid and gas-phase formation enthalpies.
- DFT calculations validate sublimation enthalpies with uncertainties under 10 kJ·mol−1.

## Abstract

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.

The graphical abstract is structured into three horizontal sections, each presenting a key concept on the left and a corresponding molecular‐scale illustration on the right. The top section shows crystal lattice models of potassium salts and conveys the solid‐state structural motifs underlying the computational approach. The middle section presents the reaction equation for the potassium formate/potassium bicarbonate equilibrium and frames this reversible reaction as a pathway for hydrogen uptake and release. The bottom section depicts potassium formate and potassium bicarbonate surrounded by hydration shells, illustrating aqueous solvation and indicating how solvation can modulate the reaction enthalpy associated with hydrogenation in solution. Together, the scheme summarizes how experimental solution calorimetry and quantum‐chemical calculations can be combined to obtain a consistent set of thermodynamic quantities for inorganic salts, including formation and sublimation enthalpies.© 2026 WILEY‐VCH GmbH