H3OION in MSE databank

Reference state properties for H3OION

H3OION was added to MSE databank about 10 years ago.

The equations used were as follows to fit the H3O data. Please note that all data used for the hydronium ion was generated using OLI software.

EQUILIBRIUM

H2O=HION+OHION

H3OION=HION+H2O

EQUATIONS

DEFINE KH3OIONE=EXP(KH3OION)

DEFINE DENGCC=0.001*DENMAS

END

The hydronium ion was added as a new species when H+ ion existed in the software too. The presence of both forms of Hydrogen ion could have affected the reference state property values and Helgeson Equation of state parameter values for Hydronium ion. By convention all ref state property and parameter values for H+ ion are assumed to be zero.

Hence

• If H3O+ = H2O + H+
• Then H3O+ = H2O

Basically in OLI software , after above mentioned fitting occurred, it was assumed that the ref state property values for hydronium ion to be equal to properties of water. However when you look at these components in ESP , you might observe a slight divergence in the values for hydronium ion from that of H2O. This is because when the data was being fit, it was tried to fit over a large range of temperature and pressure. And with above mentioned equations, it can be seen that the equilibrium constant was defined manually. Hence in the course of the data fit and K tending towards numeric value one, the ref state property values for hydronium ion diverged. But they could be safely assumed to be as closely predicted near water properties.