This keyword data block is
+used to define the binary interaction coefficients of gas components for
+Peng-Robinson gases.
+
+
+
+
Example data block
+
+
Line 0:GAS_BINARY_PARAMETERS
Line 1a:H2O(g)CO2(g)0.19
Line 1b:H2O(g)H2S(g)0.19
Line 1c:H2O(g)H2Sg(g)0.19
Line 1d:H2O(g)CH4(g)0.49
Line 1e:H2O(g)Mtg(g)0.49
Line 1f:H2O(g)Methane(g)0.49
Line 1g:H2O(g)N2(g)0.49
Line 1h:H2O(g)Ntg(g)0.49
Line 1i:H2O(g)Ethane(g)0.49
Line 1j:H2O(g)Propane(g)0.55
+
+
+
+
Explanation
+
+
Line 0: GAS_BINARY_PARAMETERS
+
+
GAS_BINARY_PARAMETERS is the keyword for the data block.
+
+
Line 1: Gas component 1, gas component 2, coefficient
+
+
Gas component 1, gas component 2–Names of the gas component pair
+for which the interaction coefficient is defined. These names are gases that
+are defined in PHASES definitions.
+
+
coefficient –Binary
+interaction coefficient for the gas-component pair.
+
+
+
+
+
+
Notes
+
+
The order of the gas-component pair is irrelevant; the same
+binary interaction coefficient applies regardless of the order in which the
+pair is defined. Previously, only interaction coefficients that were defined
+internally were used in Peng-Robinson gas calculations. The example data block
+above gives the internal, hard-coded values. The hard-coded interaction
+coefficients will still be used if they are not modified by a
+GAS_BINARY_PARAMETERS data block in the database file or the input file.
-This keyword data block is used to define a half-reaction and relative log
-K
- for each exchange species. Normally, this data block is included in the database file and only additions and modifications are included in the input file.
-
-
-Example data block
-
Line 0: EXCHANGE_SPECIES
-
Line 1a: X- = X-
-
Line 2a: log_k 0.0
-
Line 1b: X- + Na+ = NaX
-
Line 2b: log_k 0.0
-
Line 3: -gamma 4. 0.075 0.1
-
Line 1c: 2X- + Ca+2 = CaX2
-
Line 2c: log_k 0.8
-
Line 4: -davies
-
Line 1d: Xa- = Xa-
-
Line 2d: log_k 0.0
-
Line 1e: Xa- + Na+ = NaXa
-
Line 2e: log_k 0.0
-
Line 1f: 2Xa- + Ca+2 = CaXa2
-
Line 2f: log_k 2.0
-
-
-
-Explanation
-
-Line 0:
-EXCHANGE_SPECIES
-
-
-Keyword for the data block. No other data are input on the keyword line.
-
-Line 1:
-Association reaction
-
-
-Association reaction for exchange species. The defined species must be the first species to the right of the equal sign. The association reaction must precede any identifiers related to the exchange species. Master species have an identity reaction (Lines 1a and 1d).
-
-Line 2:
-log_k
-
-
-log
-K
-
-
-
-log_k
---Identifier for log
-K
- at 25 °C. Optionally,
--log_k
-,
-logk
-,
--l
-[
-og_k
-], or
--l
-[
-ogk
-].
-
-
-log K
---Log
-K
- at 25 °C for the reaction. Unlike log
-K
- for aqueous species, the log
-K
- for exchange species is implicitly relative to a reference exchange species. In the default database file, sodium (NaX) is used as the reference and the reaction X
--
- + Na
-+
- = NaX is given a log
-K
- of 0.0 (Line 2b). By subtracting the reaction for NaX in Line 1b twice from the reaction for CaX2 in Line 1c, it follows that log
-K
- for the reaction in Line 2c is numerically equal to log
-K
- for the reaction 2NaX + Ca
-+2
- = CaX
-2
- + 2Na
-+
-. The identity reaction for a master species has log
-K
- of 0.0 (Lines 2a and 2d); reactions for reference species also have log
-K
- of 0.0 (Lines 2b and 2e). Default is 0.0.
-
-Line 3:
--gamma
-
-Debye-Hückel a, Debye-Hückel b, active_fraction_coefficient
-
-
-
--gamma
---Indicates WATEQ Debye-Hückel equation will be used to calculate an activity coefficient for the exchange species if the aqueous model is an ion-association model (see
--exchange_gammas
- in the EXCHANGE data block for information about activity coefficients when using the Pitzer or SIT aqueous models). If
--gamma
- or
--davies
- is not input for an exchange species, the activity of the species is equal to its equivalent fraction. If
--gamma
- is entered, then an activity coefficient of
-
-the form of WATEQ (Truesdell and Jones, 1974),
-, is multiplied times the equivalent fraction to obtain activity for the exchange species. In this equation,
- is the activity coefficient,
- is ionic strength (mol/L [mole per liter], assumed to be equal to mol/kgw [mole per kilogram water]),
-A
- and
-B
- are constants at a given temperature and pressure,
- is the number of equivalents of exchanger in the exchange species, and
- and b are ion-specific parameters. Optionally,
-gamma
-or
- -g
-[
-amma
-].
-
-
-Debye-Hückel a
---Parameter
- ao
- in the WATEQ activity-coefficient equation.
-
-
-Debye-Hückel b
---Parameter
- b
-in the WATEQ activity-coefficient equation.
-
-
-active_fraction_coefficient
---Parameter
-
-for changing log_k as a function of the exchange sites occupied (Appelo, 1994a). The active-fraction model is useful for modeling sigmoidal exchange isotherms and proton exchange on organic matter (see http://www.hydrochemistry.eu/exmpls/a_f.html, accessed June 25, 2012).
-
-Line 4:
--davies
-
-
-
--davies
---Indicates the Davies equation will be used to calculate an activity coefficient. If
--gamma
- or
--davies
- is not input for an exchange species, the activity of the species is equal to its equivalent fraction. If
--davies
-is entered, then an activity coefficient of the form of the Davies equation,
-, is multiplied times the equivalent fraction to obtain activity for the exchange species. In this equation,
- is the activity coefficient,
- is ionic strength,
-A
- is a constant at a given temperature, and
- is the number of equivalents of exchanger in the exchange species. Optionally,
-davies
-or
- -d
-[
-avies
-].
-
-
-
-Notes
-
-Lines 1 and 2 may be repeated as necessary to define all of the exchange reactions, with Line 1 preceding Line 2 for each exchange species. One identity reaction that defines the exchange master species (in the Example data block, Lines 1a and 2a, 1d and 2d) and one reference half-reaction are needed for each exchanger. The identity reaction has a log
-K
- of 0.0. The reference half-reaction for each exchanger also will have a log
-K
- of 0.0 (in the Example data block, Lines 1b and 2b, 1e and 2e); in the default database file the reference half-reaction is Na
-+
- + X
--
- = NaX. Multiple exchangers may be defined simply by defining multiple exchange master species and additional half-reactions involving these master species, as in this Example data block.
-
-Activities of exchange species may be expressed as equivalent or mole fractions of the species (Gaines-Thomas or Vanselow convention, respectively), or as fractions of the exchange sites occupied (Gapon convention). All three conventions can be used in PHREEQC (see http://www.hydrochemistry.eu/pub/ap_pa02.pdf, accessed June 25, 2012). In the databases, the Gaines-Thomas convention is used.
-
-Cation exchange experiments with heterovalent exchange in which the salinity of the solutions is varied (for example, exchange of 2Na
-+
- for Ca2+ at varying Cl- concentrations) can be modeled better when exchange is calculated with molal concentrations for solute species instead of activities. This implies that the activity coefficients of solute cations and exchangeable species are the same, perhaps because a large part of cation exchange in soils and sediments takes part in the electrostatic double layer. Accordingly, PHREEQC permits the activity coefficient for exchangeable species to be defined in the same way as the solute species. The
--gamma
- identifier allows the equivalent fraction to be multiplied by an activity coefficient by using the WATEQ Debye-Hückel equation. Similarly, when using the
-llnl.dat
- database,
--llnl_gamma
- can be used to multiply the equivalent fraction by the activity coefficient that is defined according to the conventions of the
-llnl.dat
- database. The Davies equation can be used to calculate the activity coefficient of the exchange species by specifying the
--davies
- identifier. The use of these equations is strictly empirical and is motivated by the observation that these activity corrections provide a better fit to some experimental data.
-
-Temperature dependence of log
-K
- can be defined with the standard enthalpy of reaction (
--delta_h
-) using the Van’t Hoff equation or with an analytical expression (
--analytical_expression
-). Sometimes it is useful to offset a log K from zero for parameter fitting, or to account for dependencies among log K values, in which case the
--add_log_k
-identifier can be used to add the value defined by a named analytical expression (MIX_EQUILIBRIUM_PHASES) to the log K of the exchange species. See SOLUTION_SPECIES for examples.
-
-The identifier
--no_check
- can be used to disable checking charge and elemental balances (see SOLUTION_SPECIES) and allows the Gapon exchange convention to be used (See http://www.hydrochemistry.eu/a&p/6/exch_phr.pdf, accessed June 25, 2012).
-
-
-
-Example problems
-
-The keyword
-EXCHANGE_SPECIES
-is used in example problems 12, 13, 18, and 21. See also the databases
-Amm.dat
-,
- iso.dat
-,
- llnl.dat
-,
- phreeqc.dat
-,
- pitzer.dat
-,
-
-and
-wateq4f.dat
-.
This keyword data block
+is used to define a half-reaction and relative log K for each exchange
+species. Normally, this data block is included in the database file and only
+additions and modifications are included in the input file.
+
+
+
+
Example
+data block
+
+
Line 0:EXCHANGE_SPECIES
Line 1a:X- = X-
Line 2a:log_k0.0
Line 1b:X- + Na+ = NaX
Line 2b:log_k0.0
Line 3: -gamma4.0.0750.1
Line 1c: 2X- + Ca+2 = CaX2
Line 2c:log_k0.8
Line 4:-davies
Line 1d:Xa- = Xa-
Line 2d:log_k0.0
Line 1e:Xa- + Na+ = NaXa
Line 2e:log_k0.0
Line 1f:2Xa- + Ca+2 = CaXa2
Line 2f:log_k2.0
+
+
+
+
Explanation
+
+
Line
+0: EXCHANGE_SPECIES
+
+
Keyword for the data
+block. No other data are input on the keyword line.
+
+
Line
+1: Association reaction
+
+
Association reaction
+for exchange species. The defined species must be the first species to the
+right of the equal sign. The association reaction must precede any identifiers
+related to the exchange species. Master species have an identity reaction (Lines
+1a and 1d).
+
+
Line
+2: log_k log K
+
+
log_k
+--Identifier for log K at 25 °C. Optionally, -log_k ,
+logk , -l [
+og_k ], or -l [ogk ].
+
+
log
+K --Log K at 25 °C for the reaction. Unlike log K
+for aqueous species, the log K for exchange species is implicitly
+relative to a reference exchange species. In the default database file, sodium
+(NaX) is used as the reference and the reaction X
+- + Na + = NaX is given a log K
+of 0.0 (Line 2b). By subtracting the reaction for NaX
+in Line 1b twice from the reaction for CaX2 in Line 1c, it follows that log K
+for the reaction in Line 2c is numerically equal to log K for the
+reaction 2NaX + Ca +2 = CaX 2 +
+2Na+ .
+The identity reaction for a master species has log K of 0.0 (Lines 2a
+and 2d); reactions for reference species also have log K of 0.0 (Lines
+2b and 2e). Default is 0.0.
+
+
Line
+3: -gammaDebye-Hückel a, Debye-Hückel b, active_fraction_coefficient
+
+
+
-gamma
+--Indicates WATEQ Debye-Hückel equation will be used
+to calculate an activity coefficient for the exchange species if the aqueous
+model is an ion-association model (see -exchange_gammas
+in the EXCHANGE data block for
+information about activity coefficients when using the Pitzer or SIT aqueous
+models). If -gamma or -davies
+is not input for an exchange species, the activity of the species is equal to
+its equivalent fraction. If -gamma is entered, then an
+activity coefficient of
+
+
the
+form of WATEQ (Truesdell and Jones, 1974), ,
+is multiplied times the equivalent fraction to obtain activity for the exchange
+species. In this equation, is the activity
+coefficient, is ionic strength
+(mol/L [mole per liter], assumed to be equal to mol/kgw
+[mole per kilogram water]), A and B are constants at a given
+temperature and pressure, is the number of
+equivalents of exchanger in the exchange species, and and
+b are ion-specific parameters. Optionally, gamma or -g
+[amma ].
+
+
Debye-Hückel a --Parameterao in the WATEQ activity-coefficient equation.
+
+
Debye-Hückel b --Parameter b in
+the WATEQ activity-coefficient equation.
+
+
active_fraction_coefficient
+--Parameterfor changing log_k as a function
+of the exchange sites occupied (Appelo, 1994a). The active-fraction model is
+useful for modeling sigmoidal exchange isotherms and proton exchange on organic
+matter (see http://www.hydrochemistry.eu/exmpls/a_f.html, accessed June 25,
+2012).
+
+
Line
+4: -davies
+
+
-davies --Indicates the Davies
+equation will be used to calculate an activity coefficient. If -gamma
+or -davies is not input for an
+exchange species, the activity of the species is equal to its equivalent
+fraction. If -daviesis entered,
+then an activity coefficient of the form of the Davies equation, , is multiplied times the equivalent
+fraction to obtain activity for the exchange species. In this equation, is the activity coefficient, is ionic strength, A is a
+constant at a given temperature, and is
+the number of equivalents of exchanger in the exchange species. Optionally, daviesor -d
+[avies ].
+
+
+
+
+
+
Notes
+
+
Lines 1 and 2 may be
+repeated as necessary to define all of the exchange
+reactions, with Line 1 preceding Line 2 for each exchange species. One identity
+reaction that defines the exchange master species (in the Example data block,
+Lines 1a and 2a, 1d and 2d) and one reference half-reaction are needed for each
+exchanger. The identity reaction has a log K of 0.0. The reference
+half-reaction for each exchanger also will have a log K of 0.0 (in the
+Example data block, Lines 1b and 2b, 1e and 2e); in the default database file
+the reference half-reaction is Na + + X - = NaX. Multiple exchangers may be defined simply by defining
+multiple exchange master species and additional half-reactions involving these
+master species, as in this Example data block.
+
+
Activities of exchange
+species may be expressed as equivalent or mole fractions of the species
+(Gaines-Thomas or Vanselow convention, respectively), or as fractions of the
+exchange sites occupied (Gapon convention). All three
+conventions can be used in PHREEQC (see
+http://www.hydrochemistry.eu/pub/ap_pa02.pdf, accessed June 25, 2012). In the
+databases, the Gaines-Thomas convention is used.
+
+
Cation exchange
+experiments with heterovalent exchange in which the
+salinity of the solutions is varied (for example, exchange of 2Na +
+for Ca2+ at varying Cl- concentrations) can be modeled better when exchange is
+calculated with molal concentrations for solute species instead of activities.
+This implies that the activity coefficients of solute cations and exchangeable
+species are the same, perhaps because a large part of cation exchange in soils
+and sediments takes part in the electrostatic double layer. Accordingly,
+PHREEQC permits the activity coefficient for exchangeable species to be defined
+in the same way as the solute species. The -gamma identifier
+allows the equivalent fraction to be multiplied by an activity coefficient by
+using the WATEQ Debye-Hückel equation. Similarly,
+when using the llnl.dat database, -llnl_gamma
+can be used to multiply the equivalent fraction by the activity coefficient
+that is defined according to the conventions of the llnl.dat database.
+The Davies equation can be used to calculate the activity coefficient of the
+exchange species by specifying the -davies
+identifier. The use of these equations is strictly empirical and is motivated
+by the observation that these activity corrections provide a better fit to some
+experimental data.
+
+
Temperature dependence
+of log K can be defined with the standard enthalpy of reaction ( -delta_h
+) using the Van’t Hoff equation or with an analytical expression ( -analytical_expression ). Sometimes it is useful to
+offset a log K from zero for parameter fitting, or to account for dependencies
+among log K values, in which case the -add_log_k
+identifier can be used to add the value defined by a named analytical
+expression (MIX_EQUILIBRIUM_PHASES)
+to the log K of the exchange species. See SOLUTION_SPECIES for examples.
+
+
The identifier -no_check can be used to disable checking charge
+and elemental balances (see SOLUTION_SPECIES)
+and allows the Gapon exchange convention to be used
+(See http://www.hydrochemistry.eu/a&p/6/exch_phr.pdf, accessed June 25,
+2012).
+
+
+
+
+
+
Example
+problems
+
+
The keyword EXCHANGE_SPECIES
+is used in example problems 12,
+13, 18, and 21. See also the databases Amm.dat , iso.dat , llnl.dat ,
+phreeqc.dat , pitzer.dat ,and wateq4f.dat .
-This keyword data block is used to define the composition of a fixed-total-pressure or a fixed-volume multicomponent gas phase. The thermodynamic properties of the gas components are defined with PHASES input. If the critical pressure and temperature are defined for a gas component with PHASES, the Peng-Robinson equation of state (EOS) will be used for calculating the relation between pressure and molar volume, and fugacity coefficients will be calculated for the gases. If the critical temperature and pressure are not defined, the ideal gas law will be used. Ideal gases and Peng-Robinson gases cannot be mixed in a GAS_PHASE. A GAS_PHASE data block is not needed if fixed partial pressures of gas components are desired; use EQUILIBRIUM_PHASES instead. The gas phase defined with this keyword data block subsequently may be equilibrated with an aqueous phase in combination with pure-phase, surface, exchange, and solid-solution assemblages in batch-reaction calculations. Either Henry’s law (ideal gases) or the Peng-Robinson EOS (nonideal gases) is used for calculating the solubility of the gases. As a consequence of batch reactions, a fixed-pressure gas phase may exist or not, depending on the sum of the partial pressures of the dissolved gases in solution. A fixed-volume gas phase always contains some amount of each gas component that is present in solution. The initial composition of a fixed-pressure gas phase is defined by the partial pressures of each gas component. The initial composition of a fixed-volume gas may be defined by the partial pressures of each gas component or may be defined to be that which is in equilibrium with a fixed-composition aqueous phase. When the Peng-Robinson EOS is used and the
-GAS_PHASE
-has a pressure higher than about 10 atmospheres, the initial gas-phase composition calculated for a fixed-composition aqueous phase is only an approximation of the true gas composition.
-
-number
---A positive number designates the gas phase and its composition. A range of numbers may also be given in the form
-m
--
-n
-, where
-m
- and
-n
- are positive integers,
-m
- is less than
-n
-, and the two numbers are separated by a hyphen without intervening spaces. Default is 1.
-
-
-description
---Optional comment that describes the gas phase.
-
-Line 1:
--fixed_pressure
-
-
-
--fixed_pressure
---Identifier defining the gas phase to have a fixed total pressure; that is, a gas bubble. A fixed-pressure gas phase is the default if neither the
--fixed_pressure
- nor the
--fixed_volume
- identifier is used. Optionally
-fixed_pressure
- or
--fixed_p
-[
-ressure
-].
-
-Line 2:
--pressure
-
- pressure
-
-
-
--pressure
---Identifier defining the fixed pressure of the gas phase that applies during all batch-reaction and transport calculations. Optionally
-pressure
- or
--p
-[
-ressure
-].
-
-
-pressure
---The pressure of the gas phase, in atm (atmosphere). Default is 1.0 atm.
-
-Line 3:
--volume
-
-volume
-
-
-
--volume
---Identifier defining the initial volume of the fixed-pressure gas phase. Optionally,
-volume
- or
--v
-[
-olume
-].
-
-
-volume
---The initial volume of the fixed-pressure gas phase, in liters. The ideal gas law or the Peng-Robinson EOS is used to calculate the initial moles, n, of each gas component in the fixed-pressure gas phase. Default is 1.0 L (liter).
-
-Line 4:
--temperature
-
-temp
-
-
-
--temperature
---Identifier defining the initial temperature of the gas phase. Optionally,
-temperature
- or
--t
-[
-emperature
-].
-
-
-temp
---The initial temperature of the gas phase, in °C (degree Celsius). The
-temp
- along with
-volume
- and
-partial pressure
- are used to calculate the initial moles of each gas component in the fixed-pressure gas phase. Default is 25.0 °C.
-
-Line 5:
-phase name, partial pressure
-
-
-
-phase name
---Name of a gas component. A phase with this name must be defined by PHASES input in the database or input file.
-
-
-partial pressure
---Initial partial pressure of this component in the gas phase (atm). The
-partial pressure
- along with
-volume
- and
-temp
- are used to calculate the initial moles of this gas component in the fixed-pressure gas phase.
-
-
-
-Notes 1
-
-Line 5 must be repeated as necessary to define all of the components initially present in the fixed-pressure gas phase as well as any components which may subsequently enter the gas phase. The initial moles of a gas component that is defined to have a positive partial pressure in
-GAS_PHASE
- input will be computed using either the ideal gas law,
-n = PV/RT
-, where
-n
- is the moles of the gas,
-P
- is the defined partial pressure (Line 5),
-V
- is the initial volume, given by
--volume
-, R is the gas constant (0.08207 L K
--1
-mol
--1
-, liter per degree kelvin per mole), and
-T
- is given by
--temperature
-(converted to kelvin), or the Peng-Robinson EOS (see keyword PHASES for the equations). Thus, in Example data block 1 and with the wateq4f.dat database, which does not define critical temperatures and pressures, the moles of all gases are calculated by n = (0.000316 + 0.2 + 0.78)
-×
- 1.0 / (298
-×
- 0.02807) = 0.04 mol.
-If this gas phase reacts with a solution with a very small amount of water so that n does not change (that is, the dissolution of gas is negligible), the volume becomes V =
-0.04
-×
- (298
-×
- 0.02807) / 1.001 = 0.979 L. It is likely that the sum of the partial pressures of the defined gases will not be equal to the pressure given by
--pressure
-. However, when the
-GAS_PHASE
- reacts with a solution during a batch-reaction simulation, the moles of gases and volume of the gas phase will be adjusted so that each component is in equilibrium with the solution while the total pressure (sum of the partial pressures) is that specified by
--pressure
-. It is possible that the gas phase disappears if the sum of the partial pressures of dissolved gases is less than the pressure given by
--pressure
-.
-
-A gas component may be defined to have initial partial pressure of zero. In this case, no moles of that component will be present initially, but the component may enter the gas phase when in contact with a solution that contains that component. If no gas phase exists initially, the initial partial pressures of all components should be set to 0.0; a gas phase may subsequently form if batch reactions cause the sum of the partial pressures of the gas components to exceed
-pressure
-.
-
-
-
-Example data block 2
-
Line 0: GAS_PHASE 1-5 Find composition from solution 1
-
-number
---a positive number designates the gas phase and its composition. A range of numbers may also be given in the form
-m
--
-n
-, where
-m
- and
-n
- are positive integers,
-m
- is less than
-n
-, and the two numbers are separated by a hyphen without intervening spaces. Default is 1.
-
-
-description
---Optional comment that describes the gas phase.
-
-Line 1:
--fixed_volume
-
-
-
--fixed_volume
---Identifier defining the gas phase to be one that has a fixed volume (not a gas bubble). A fixed-pressure gas phase is the default if neither the
--fixed_pressure
- nor the
--fixed_volume
- identifier is used. Optionally
-fixed_volume
- or
--fixed_v
-[
-olume
-].
-
-Line 2:
--volume
-
-volume
-
-
-
--volume
---Identifier defining the volume of the fixed-volume gas phase, which applies for all batch-reaction or transport calculations. Optionally,
-volume
- or
--v
-[
-olume
-].
-
-
-volume
---The volume of the fixed-volume gas phase, in liters. Default is 1.0 L.
-
-Line 3:
--temperature
-
-temp
-
-
-
--temperature
---Identifier defining the initial temperature of the gas phase. Optionally,
-temperature
- or
--t
-[
-emperature
-].
-
-
-temp
---The initial temperature of the gas phase, in °C. Default is 25.0 °C.
-
-Line 4:
-phase name, partial pressure
-
-
-
-phase name
---Name of a gas component. A phase with this name must be defined by PHASES input in the database or input file.
-
-
-partial pressure
---Initial partial pressure of this component in the gas phase, in atm. The
-partial pressure
- along with
-volume
- and
-temp
- are used to calculate the initial moles of this gas component in the fixed-volume gas phase.
-
-
-
-Notes 2
-
-Line 4 may be repeated as necessary to define all the components initially present in the fixed-volume gas phase, as well as any components which may subsequently enter the gas phase. The initial moles of a gas component with a positive partial pressure will be computed using either the ideal gas law,
-n = PV/(RT)
-, where
-n
- is the moles of the gas,
-P
- is the defined partial pressure (Line 4),
-V
- is given by
--volume
-, R is the gas constant, and
-T
- is given by
--temperature
-(converted to kelvin), or the Peng-Robinson EOS. When the gas phase reacts with a solution during a batch-reaction simulation, the total pressure, the partial pressures of the gas components in the gas phase, and the partial pressures of the gas components in the aqueous phase will be adjusted so that equilibrium is established for each component. A constant-volume gas phase always exists unless all of the gas components are absent from the system. The identifier
--pressure
-is not used for a fixed-volume gas phase.
-
-A gas component may be defined to have an initial partial pressure of zero. In this case, no moles of that component will be present initially, but the component will enter the gas phase when in contact with a solution containing the component.
-
-number
---A positive number designates the gas phase and its composition. A range of numbers may also be given in the form
-m
--
-n
-, where
-m
- and
-n
- are positive integers,
-m
- is less than
-n
-, and the two numbers are separated by a hyphen without intervening spaces. Default is 1.
-
-
-description
---Optional comment that describes the gas phase.
-
-Line 1:
--fixed_volume
-
-
-
--fixed_volume
---Identifier defining the gas phase to be one that has a fixed volume (not a gas bubble). A fixed-pressure gas phase is the default if neither the
--fixed_pressure
- nor the
--fixed_volume
- identifier is used. Optionally
-fixed_volume
- or
--fixed_v
-[
-olume
-].
-
-Line 2:
--equilibrate
-
- number
-
-
-
--equilibrate
---Identifier indicates that the fixed-volume gas phase is defined to be in equilibrium with a solution of a fixed composition. This identifier may only be used with the
--fixed_volume
- identifier. Optionally,
-equil
-,
- equilibrium
-,
--e
-[
-quilibrium
-],
-equilibrate
-,
--e
-[
-quilibrate
-].
-
-
-number
---Solution number with which the fixed-volume gas phase is to be in equilibrium. Any alphabetic characters following the identifier and preceding an integer (“with solution” in Line 2) are ignored.
-
-Line 3:
--volume
-
-volume
-
-
-
--volume
---Identifier defining the volume of the fixed-volume gas phase, which applies for all batch-reaction or transport calculations. Optionally,
-volume
- or
--v
-[
-olume
-].
-
-
-volume
---The volume of the fixed-volume gas phase, L. Default is 1.0 L.
-
-Line 4:
-phase name
-
-
-
-phase name
---Name of a gas component. A phase with this name must be defined by PHASES input in the database or input file.
-
-
-
-Notes 3
-
-Line 4 may be repeated as necessary to define all of the components that may be present in the fixed-volume gas phase. The
--equilibrate
- identifier specifies that the initial moles of the gas components are to be calculated by equilibrium with solution 10. This calculation is termed an “initial gas-phase-composition calculation”. During this calculation, the composition of solution 10 does not change, only the moles of each component in the gas phase are calculated. This calculation is approximate for a Peng-Robinson GAS_PHASE due to the fugacity coefficient, which is used for calculating the activity of the gas in the solubility equation. Alternatively, for Peng-Robinson gases, keyword GAS_PHASE_MODIFY may be used, but this is still approximate for a gas-mixture at high pressure. A constant-volume gas phase always exists unless all of the gas components are absent from the system. When the
--equilibrate
- identifier is used, the identifiers
--pressure
- and
--temperature
-are not needed and initial partial pressures for each gas component need not be specified; the partial pressures for the gas components are calculated from the partial pressures in solution and the temperature is equal to the solution temperature. The
--equilibrate
- identifier cannot be used with a fixed-pressure gas phase.
-
-A gas component may have an initial partial pressure of zero because the solution with which the gas phase is in equilibrium does not contain that gas component. In this case, no moles of that component will be present initially, but the component may enter the gas phase when the gas is in contact with another solution that does contain that component.
-
-After a batch reaction has been simulated, it is possible to save the resulting gas-phase composition with the SAVE keyword. If the new composition is not saved, the gas-phase composition will remain the same as it was before the batch reaction. After it has been defined or saved, the gas phase can be used in subsequent simulations through the USE keyword. TRANSPORT and
-ADVECTION
-
-
- calculations automatically update the gas-phase composition and SAVE has no effect during these calculations.
-
-
-
-Example problems
-
-The keyword
-GAS_PHASE
-is used in example problems 7 and 22.
This keyword data block is
+used to define the composition of a fixed-total-pressure or a fixed-volume
+multicomponent gas phase. The thermodynamic properties of the gas components
+are defined with PHASES input. If
+the critical pressure and temperature are defined for a gas component with PHASES, the Peng-Robinson equation of
+state (EOS) will be used for calculating the relation between pressure and
+molar volume, and fugacity coefficients will be calculated for the gases. If
+the critical temperature and pressure are not defined, the ideal gas law will
+be used. Ideal gases and Peng-Robinson gases cannot be mixed in a GAS_PHASE. A GAS_PHASE data block is not needed if
+fixed partial pressures of gas components are desired; use EQUILIBRIUM_PHASES instead. The gas
+phase defined with this keyword data block subsequently may be equilibrated
+with an aqueous phase in combination with pure-phase, surface, exchange, and
+solid-solution assemblages in batch-reaction calculations. Either Henry’s law
+(ideal gases) or the Peng-Robinson EOS (nonideal gases) is used for calculating
+the solubility of the gases. As a consequence of batch reactions, a
+fixed-pressure gas phase may exist or not, depending on the sum of the partial
+pressures of the dissolved gases in solution. A fixed-volume gas phase always
+contains some amount of each gas component that is present in solution. The
+initial composition of a fixed-pressure gas phase is defined by the partial
+pressures of each gas component. The initial composition of a fixed-volume gas
+may be defined by the partial pressures of each gas component or may be defined
+to be that which is in equilibrium with a fixed-composition aqueous phase. When
+the Peng-Robinson EOS is used and the GAS_PHASE has a pressure
+higher than about 10 atmospheres, the initial gas-phase composition calculated
+for a fixed-composition aqueous phase is only an approximation of the true gas
+composition.
+
+
+
+
Example data block 1
+
+
Line 0:GAS_PHASE 1-5Air
Line 1:-fixed_pressure
Line 2:-pressure1.001
Line 3:-volume1.0
Line 4:-temperature25.0
Line 5a:CH4(g)0.0
Line 5b:CO2(g)0.000316
Line 5c:O2(g)0.2
Line 5d:N2(g)0.78
+
+
+
+
Explanation 1
+
+
Line 0: GAS_PHASE [ number ] [ description ]
+
+
GAS_PHASE is the
+keyword for the data block.
+
+
number --A positive number
+designates the gas phase and its composition. A range of numbers may also be
+given in the form m - n ,
+where m and n are positive integers, m is less than n
+, and the two numbers are separated by a hyphen without intervening spaces.
+Default is 1.
+
+
description --Optional comment that
+describes the gas phase.
+
+
Line 1: -fixed_pressure
+
+
+
-fixed_pressure --Identifier defining the gas phase to have a fixed total
+pressure; that is, a gas bubble. A fixed-pressure gas phase is the default if
+neither the -fixed_pressure nor the -fixed_volume identifier is used. Optionally fixed_pressure or -fixed_p [ressure ].
+
+
Line 2: -pressurepressure
+
+
+
-pressure
+--Identifier defining the fixed pressure of the gas phase that applies during
+all batch-reaction and transport calculations. Optionally pressure
+or -p [ressure ].
+
+
pressure --The pressure of the gas
+phase, in atm (atmosphere). Default is 1.0 atm.
+
+
Line 3: -volume volume
+
+
+
-volume --Identifier defining the
+initial volume of the fixed-pressure gas phase. Optionally, volume
+or -v [olume ].
+
+
volume --The initial volume of the
+fixed-pressure gas phase, in liters. The ideal gas law or the Peng-Robinson EOS
+is used to calculate the initial moles, n, of each gas component in the
+fixed-pressure gas phase. Default is 1.0 L (liter).
+
+
Line 4: -temperature temp
+
+
-temperature
+--Identifier defining the initial temperature of the gas phase. Optionally, temperature
+or -t [emperature ].
+
+
temp --The initial temperature of
+the gas phase, in °C (degree Celsius). The temp along with volume
+and partial pressure are used to calculate the initial moles of each
+gas component in the fixed-pressure gas phase. Default is 25.0 °C.
+
+
Line 5: phase name, partial pressure
+
+
phase name --Name
+of a gas component. A phase with this name must be defined by PHASES input in the database or input
+file.
+
+
partial pressure --Initial
+partial pressure of this component in the gas phase (atm). The partial
+pressure along with volume and temp are used to
+calculate the initial moles of this gas component in the fixed-pressure gas
+phase.
+
+
+
+
+
+
Notes 1
+
+
Line 5 must be repeated as necessary to define all of the
+components initially present in the fixed-pressure gas phase as well as any
+components which may subsequently enter the gas phase. The initial moles of a
+gas component that is defined to have a positive partial pressure in GAS_PHASE
+input will be computed using either the ideal gas law, n = PV/RT ,
+where n is the moles of the gas, P is the defined partial
+pressure (Line 5), V is the initial volume, given by -volume
+, R is the gas constant (0.08207 L K -1 mol -1 , liter
+per degree kelvin per mole), and T is given by -temperature (converted
+to kelvin), or the Peng-Robinson EOS (see keyword PHASES for the equations). Thus, in
+Example data block 1 and with the wateq4f.dat database, which does not define
+critical temperatures and pressures, the moles of all gases are calculated by n
+= (0.000316 + 0.2 + 0.78) × 1.0 / (298 × 0.02807) = 0.04 mol.
+If this gas phase reacts with a solution with a very small amount of water
+so that n does not change (that is, the dissolution of gas is negligible), the
+volume becomes V = 0.04 × (298 × 0.02807) / 1.001 =
+0.979 L. It is likely that the sum of the partial pressures of the defined
+gases will not be equal to the pressure given by -pressure . However, when the GAS_PHASE
+reacts with a solution during a batch-reaction simulation, the moles of gases
+and volume of the gas phase will be adjusted so that each component is in
+equilibrium with the solution while the total pressure (sum of the partial
+pressures) is that specified by -pressure . It is possible that the gas phase
+disappears if the sum of the partial pressures of dissolved gases is less than
+the pressure given by -pressure .
+
+
A gas component may be defined to have initial partial pressure of
+zero. In this case, no moles of that component will be present initially, but
+the component may enter the gas phase when in contact with a solution that
+contains that component. If no gas phase exists initially, the initial partial
+pressures of all components should be set to 0.0; a gas phase may subsequently
+form if batch reactions cause the sum of the partial pressures of the gas
+components to exceed pressure .
+
+
+
+
+
+
Example data block 2
+
+
Line 0:GAS_PHASE 1-5Find composition from solution 1
Line 1:-fixed_volume
Line 2:-volume1.0
Line 3:-temperature25.0
Line 4a:CH4(g)0.0
Line 4b:CO2(g)0.000316
Line 4c:O2(g)0.2
Line 4d:N2(g)0.78
+
+
+
+
Explanation 2
+
+
Line 0: GAS_PHASE [ number ] [ description ]
+
+
GAS_PHASE is the
+keyword for the data block.
+
+
number --a positive number
+designates the gas phase and its composition. A range of numbers may also be
+given in the form m - n ,
+where m and n are positive integers, m is less than n
+, and the two numbers are separated by a hyphen without intervening spaces.
+Default is 1.
+
+
description --Optional comment that
+describes the gas phase.
+
+
Line 1: -fixed_volume
+
+
-fixed_volume --Identifier defining the gas phase to be one that has a fixed
+volume (not a gas bubble). A fixed-pressure gas phase is the default if neither
+the -fixed_pressure nor the -fixed_volume identifier is used. Optionally fixed_volume or -fixed_v [olume ].
+
+
Line 2: -volume volume
+
+
+
-volume --Identifier defining the
+volume of the fixed-volume gas phase, which applies for all batch-reaction or
+transport calculations. Optionally, volume or -v
+[olume ].
+
+
volume --The volume of the
+fixed-volume gas phase, in liters. Default is 1.0 L.
+
+
Line 3: -temperature temp
+
+
-temperature
+--Identifier defining the initial temperature of the gas phase. Optionally, temperature
+or -t [emperature ].
+
+
temp --The initial temperature of
+the gas phase, in °C. Default is 25.0 °C.
+
+
Line 4: phase name, partial pressure
+
+
phase name --Name
+of a gas component. A phase with this name must be defined by PHASES input in the database or input
+file.
+
+
partial pressure --Initial
+partial pressure of this component in the gas phase, in atm. The partial
+pressure along with volume and temp are used to
+calculate the initial moles of this gas component in the fixed-volume gas
+phase.
+
+
+
+
+
+
Notes 2
+
+
Line 4 may be repeated as necessary to define all the components
+initially present in the fixed-volume gas phase, as well as any components
+which may subsequently enter the gas phase. The initial moles of a gas
+component with a positive partial pressure will be computed using either the
+ideal gas law, n = PV/(RT) ,
+where n is the moles of the gas, P is the defined partial
+pressure (Line 4), V is given by -volume , R is the
+gas constant, and T is given by -temperature (converted
+to kelvin), or the Peng-Robinson EOS. When the gas phase reacts with a solution
+during a batch-reaction simulation, the total pressure, the partial pressures
+of the gas components in the gas phase, and the partial pressures of the gas
+components in the aqueous phase will be adjusted so that equilibrium is
+established for each component. A constant-volume gas phase always exists
+unless all of the gas components are absent from the system. The identifier -pressure
+is not used for a fixed-volume gas phase.
+
+
A gas component may be defined to have an initial partial pressure
+of zero. In this case, no moles of that component will be present initially,
+but the component will enter the gas phase when in contact with a solution
+containing the component.
+
+
+
+
+
+
Example data block 3
+
+
Line 0:GAS_PHASE 1-5Air
Line 1:-fixed_volume
Line 2:-equilibrate with solution 10
Line 3:-volume1.0
Line 4a:CH4(g)
Line 4b:CO2(g)
Line 4c:O2(g)
Line 4d:N2(g)
+
+
+
+
Explanation 3
+
+
Line 0: GAS_PHASE [ number ] [ description ]
+
+
GAS_PHASE is the
+keyword for the data block.
+
+
number --A positive number
+designates the gas phase and its composition. A range of numbers may also be
+given in the form m - n ,
+where m and n are positive integers, m is less than n
+, and the two numbers are separated by a hyphen without intervening spaces.
+Default is 1.
+
+
description --Optional comment that
+describes the gas phase.
+
+
Line 1: -fixed_volume
+
+
-fixed_volume --Identifier defining the gas phase to be one that has a fixed
+volume (not a gas bubble). A fixed-pressure gas phase is the default if neither
+the -fixed_pressure nor the -fixed_volume identifier is used. Optionally fixed_volume or -fixed_v [olume ].
+
+
Line 2: -equilibratenumber
+
+
-equilibrate
+--Identifier indicates that the fixed-volume gas phase is defined to be in
+equilibrium with a solution of a fixed composition. This identifier may only be
+used with the -fixed_volume
+identifier. Optionally, equil ,
+equilibrium , -e [quilibrium
+], equilibrate , -e [quilibrate ].
+
+
number --Solution number with which
+the fixed-volume gas phase is to be in equilibrium. Any alphabetic characters
+following the identifier and preceding an integer (“with solution” in Line 2)
+are ignored.
+
+
Line 3: -volume volume
+
+
+
-volume --Identifier defining the
+volume of the fixed-volume gas phase, which applies for all batch-reaction or
+transport calculations. Optionally, volume or -v
+[olume ].
+
+
volume --The volume of the
+fixed-volume gas phase, L. Default is 1.0 L.
+
+
Line 4: phase name
+
+
phase name --Name
+of a gas component. A phase with this name must be defined by PHASES input in the database or input
+file.
+
+
+
+
+
+
Notes 3
+
+
Line 4 may be repeated as necessary to define all of the
+components that may be present in the fixed-volume gas phase. The -equilibrate
+identifier specifies that the initial moles of the gas components are to be
+calculated by equilibrium with solution 10. This calculation is termed an
+“initial gas-phase-composition calculation”. During this calculation, the
+composition of solution 10 does not change, only the moles of each component in
+the gas phase are calculated. This calculation is approximate for a
+Peng-Robinson GAS_PHASE due to the
+fugacity coefficient, which is used for calculating the activity of the gas in
+the solubility equation. Alternatively, for Peng-Robinson gases, keyword GAS_PHASE_MODIFY may be used, but
+this is still approximate for a gas-mixture at high pressure. A constant-volume
+gas phase always exists unless all of the gas components are absent from the
+system. When the -equilibrate identifier is used, the
+identifiers -pressure and -temperature are
+not needed and initial partial pressures for each gas component need not be
+specified; the partial pressures for the gas components are calculated from the
+partial pressures in solution and the temperature is equal to the solution
+temperature. The -equilibrate identifier cannot be used with a
+fixed-pressure gas phase.
+
+
A gas component may have an initial partial pressure of zero
+because the solution with which the gas phase is in equilibrium does not
+contain that gas component. In this case, no moles of that component will be
+present initially, but the component may enter the gas phase when the gas is in
+contact with another solution that does contain that component.
+
+
After a batch reaction has been simulated, it is possible to save
+the resulting gas-phase composition with the SAVE keyword. If the new composition
+is not saved, the gas-phase composition will remain the same as it was before
+the batch reaction. After it has been defined or saved, the gas phase can be
+used in subsequent simulations through the USE keyword. TRANSPORT and ADVECTION calculations
+automatically update the gas-phase composition and SAVE has no effect during these
+calculations.
+
+
+
+
+
+
Example problems
+
+
The keyword GAS_PHASE is used in example problems
+7 and 22.
-, is multiplied times the equivalent fraction to obtain activity for the exchange species. In this equation, 
- is the activity coefficient, 
- is ionic strength (mol/L [mole per liter], assumed to be equal to mol/kgw [mole per kilogram water]),
-A
- and
-B
- are constants at a given temperature and pressure, 
- is the number of equivalents of exchanger in the exchange species, and 
- and b are ion-specific parameters. Optionally,
-gamma
-or
- -g
-[
-amma
-].
-, is multiplied times the equivalent fraction to obtain activity for the exchange species. In this equation, 
- is the activity coefficient, 
- is ionic strength,
-A
- is a constant at a given temperature, and 
- is the number of equivalents of exchanger in the exchange species. Optionally,
-davies
-or
- -d
-[
-avies
-].