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This keyword is used to define a name, chemical reaction, and log K for each mineral and pure gas that is used for saturation-index calculations, reaction-path, transport, or inverse-modeling calculations. Normally, this data block is included in the database file and only additions and modifications are included in the input file.


Line 0:  PHASES 
Line 1a: Gypsum
Line 2a:      CaSO4:2H2O = Ca+2 + SO4-2 + 2H2O
Line 3a:      log_k     -4.58
Line 4a:      delta_h   -0.109
Line 5:       -analytical_expression 68.2401 0.0 -3221.51  -25.0627  0.0
Line 1b: O2(g)
Line 2b:      O2 = O2
Line 3b:      log_k     -2.96
Line 4b:      delta_h   1.844


Line 0: PHASES

Keyword for the data block. No other data are input on the keyword line.

Line 1: Phase name

phase name--alphanumeric name of phase, no spaces are allowed.

Line 2: Dissolution reaction

Dissolution reaction for phase to aqueous species. Any aqueous species, including e-, may be used in the dissolution reaction. The chemical formula for the defined phase must be the first chemical formula on the left-hand side of the equation. The dissolution reaction must precede any identifiers related to the phase. The stoichiometric coefficient for the phase must be 1.0.

Line 3: log_k log K

log_k--Identifier for log K at 25oC. Optionally, -log_k, logk, -l[og_k], or -l[ogk].

log K--Log K at 25oC for the reaction. Default 0.0.

Line 4: delta_h enthalpy, units

delta_h--Identifier for enthalpy of reaction at 25oC. Optionally, -delta_h, deltah, -d[elta_h], or -d[eltah].

enthalpy--enthalpy of reaction at 25oC for the reaction. Default 0.0.

units--Default units are kilojoules per mole. Units may be calories, kilocalories, joules, or kilojoules per mole. Only the energy unit is needed (per mole is implied) and abbreviations of these units are acceptable. Explicit definition of units for all enthalpy values is recommended. The enthalpy of reaction is used in the van't Hoff equation to determine the temperature dependence of the equilibrium constant. Internally, all enthalpy calculations are performed in the units of kilojoules per mole.

Line 5: -analytical_expression A1, A2, A3, A4, A5

-analytical_expression--Identifier for coefficients for an analytical expression for the temperature dependence of log K. Optionally, analytical_expression, a_e, ae, -a[nalytical_expression], -a[_e], -a[e].

A1, A2, A3, A4, A5--Five values defining log K as a function of temperature in the expression , where T is in Kelvin.


The set of lines 1 and 2 must be entered in order, either line 3 (log_k) or 5 (-analytical_expression) must be entered for each phase. Lines 3, 4, and 5 may be entered as needed in any order. Additional sets of lines 1 through 5 may be added as necessary to define all minerals and gases. The equations for the phases may be written in terms of any aqueous chemical species, including e-.

The identifiers -no_check can be used to disable checking charge and elemental balances (see SOLUTION_SPECIES). The use of -no_check is not recommended, except in cases where the phase is only to be used for inverse modeling. Even in this case, equations defining phases should be charge balanced.

Example problems

The keyword PHASES is used in example problems 1, 8, 11, and 12.

Related keywords

EQUILIBRIUM_PHASES, INVERSE_MODELING, REACTION, SAVE equilibrium_phases, and USE equilibrium_phases.

Example problems
Related keywords

User's Guide to PHREEQC - 07 MAY 96
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