Classical simulation of acid and base dissociation constants in supercritical water at constant density

Molecular dynamics simulations were performed to investigate the dissociations of water, NaOH and HCl in water at constant density of 0.9 g cm−3 at near-critical and supercritical temperatures. Results were in good qualitative agreement with available data, showing increased temperature favouring all dissociations. The dissociation of water was favoured by more negative values of U/T and an increasing entropy tem, whereas the dissociation of HCl showed both decreasing U/T and entropy. NaOH showed an increasing value of U/T which was dominated by an increasing entropy term. Differences in the energy contributions were attributed to the change in solute charges upon dissociation.