PhreeqcUsers Discussion Forum

Beginners => PHREEQC basics => Topic started by: elham on July 30, 2018, 12:28:18 PM

Title: equilibrium constant
Post by: elham on July 30, 2018, 12:28:18 PM
Hello all
I want to have amount of equilibrium constants base on temperature in phreeqc output but I don't know how. please guide me.
Thanks.
Title: Re: equilibrium constant
Post by: dlparkhurst on July 30, 2018, 03:24:50 PM
The PHASES data block contains definitions that include the equilibrium constant. Temperature dependence of the constants is defined either with a enthalpy of reaction (and the Van't Hoff expression) or with an analytical expression. When a calculation is made, the temperature of the solution or a definition by REACTION_TEMPERATURE determines the temperature for evaluation of the equilibrium constant.

The same logic applies to aqueous species, exchange species, and surface species.

The following will calculate equilibrium of gypsum (and the log K) at three temperatures:
Code: [Select]
SOLUTION
EQUILIBRIUM_PHASES
Gypsum 0 10
REACTION_TEMPERATURE
10 25 40
END
Title: Re: equilibrium constant
Post by: elham on August 01, 2018, 10:12:37 AM
thank you for you're answer.
 if I want to have amount of equilibrium constant for a reaction that exit in the databases for a different temperature what should I do? for example amount of equilibrium constant for the reaction CO3-2 + H+ = HCO3-
in the database is equal to 10^10.329 but I want the value of it at different temperatures.
thanks.
Title: Re: equilibrium constant
Post by: dlparkhurst on August 01, 2018, 06:04:44 PM
You can either evaluate the analytical expression or Van't Hoff expression at the desired temperature, or you can print the value of the equilibrium constant with USER_PRINT or USER_PUNCH by using the basic functions

LK_PHASE("Calcite") or LK_SPECIES("HCO3-"), for example, see documentation of the Basic Interpreter.
Title: Re: equilibrium constant
Post by: elham on August 05, 2018, 02:32:32 PM
thank you indeed.