  There are two main methods of calculating the thermodynamic properties of
water and solutes: mass action (including the Helgeson-Kirkham-Flowers (HKF)
equations of state and model) and Gibbs free energy minimization (e.g. Leal et
al., 2016). However, in certain regions of pressure and temperature the HKF
model inaccurately predicts the speciation and concentration of solutes (e.g.
Miron et al., 2019). The Deep Earth Water (DEW) model uses a series of HKF-type
equations to calculate the properties of water and solute concentrations at
high temperatures (373 - 1473 K) and pressures (0.1 - 6 GPa) (e.g. Huang and
Sverjensky, 2019; Pan et al., 2013; Sverjensky et al., 2014). The DEW model is
synthesized in an Excel spreadsheet and calculates Gibbs energies of formation,
equilibrium constants, and standard volume changes for reactions. Here we
present an object-oriented Python implementation of the DEW model, called
DEWPython. Our model expands on DEW by increasing model efficiency,
streamlining the input process, and incorporating SUPCRT in-line. Additionally,
our model builds in minerals and aqueous species from the thermodynamic
database slop16.dat (Boyer, 2019) which would normally be calculated
separately. We also present a set of reactions relevant to icy ocean world
interiors calculated with the DEWPython. The favorability of these reactions
indicates likely formation of certain organic species under extreme pressures
relevant to ocean worlds.
