Water
The logK° values in “Chemical Equilibrium Diagrams”
are given for infinitely diluted aqueous solutions (zero
ionic strength).
Water (H2O)
will be in excess and its activity may be considered to be constant. Therefore one
may set the activity of H2O = 1
(log activity = 0).
Water can then be ignored in chemical equilibrium calculations.
However, water (H2O) might be needed as a component if you wish
to model ionic medium effects, especially on systems where minerals precipitate
involving H2O, such as gypsum
(CaSO4·2H2O). In such cases you will need
H2O included as a component.
Therefore, when entering data for a database,
you must include H2O in the reactions.
