code: def proton_hydroxide_free_energy(temperature, pressure, pH):
      
      H2 = GasMolecule('H2')
      H2O = GasMolecule('H2O')
      G_H2 = H2.get_free_energy(temperature = temperature, pressure = pressure)
      G_H2O = H2O.get_free_energy(temperature = temperature)
      G_H = (0.5*G_H2) - ((R*temperature)/(z*F))*ln10*pH
      G_OH = G_H2O - G_H  # Do not need Kw when water equilibrated
      return(G_H, G_OH)
docs: Returns the Gibbs free energy of proton in bulk solution.
  
      Parameters
      ----------
      pH : pH of bulk solution
      temperature : numeric
          temperature in K
      pressure : numeric
         pressure in mbar
  
      Returns
      -------
      G_H, G_OH : Gibbs free energy of proton and hydroxide.