Outputs for Aqueous Solution Calculations

Results of the equilibration are output to the screen in normal, verbose, form. The various types of information presented are summarised below.

• Program Information: The value of "iFail" gives the level of confidence in the solution. A value of 0 indicates complete success. Experience shows that 6 and 1 also occur for correct answers. If iFail takes other values then the result is doubtful - please contact the authors.
• Ambient Conditions: system pressure (set to 1 atm where not available as an input for the user), ambient temperature and relative humidity are given. The equivalent partial pressure of water is also listed.
• Aqueous Phase: the molalities and activity coefficients of all solute species are listed, including the following ions and uncharged solutes that can be formed from association/dissociation reactions: HSO₄⁻, HCO₃⁻, aqueous CO₂, CaCO₃°, MgCO₃°, and MgOH⁺.

  All solute activity coefficients are on a molality basis, in contrast to the output for Models I - IV, and are relative to a reference state of infinite dilution in water (for which they are equal to unity). See Clegg et al. (J. Phys. Chem. 96, 9470-9479, 1992) for definitions, and expressions for conversion between molality and mole fraction bases.

• Gases: equilibrium partial pressures of water and any trace gases over the aqueous phase are shown. These are determined from liquid phase activities and the relevent equilibrium constants. The value for water should be equal to that given under "Ambient Conditions" above. For problems in which H₂O dissociation has been switched off, and for which the input solution has neutral pH, the equilibrium vapour pressures of acid gases are not calculated (because the hydrogen ion activity is unknown).
• Solids: the program does not determine the amounts of solids (if any) present at thermodynamic equilibrium, but instead calculates the saturation ratio of each solid phase that can form. For electrolytes, this is defined as the activity product of the ions (which constitute the solid) in solution, divided by the activity product in a solution saturated with respect to the solid. Thus the ratio for a solid that is undersaturated in solution will be less than unity, and one that is supersaturated will have a ratio greater than unity.