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Beginners => PHREEQC basics => Topic started by: paznativ on August 29, 2019, 07:16:04 AM

Title: Fixed solution volume
Post by: paznativ on August 29, 2019, 07:16:04 AM
Hello all
I would like to model a closed container, meaning, fixed total volume of gas and solution (say, total of 2 liter).
is there a way to set this? is there a way to set the maximum volume of a solution?
thank you all in advance

Paz Nativ
Title: Re: Fixed solution volume
Post by: dlparkhurst on August 29, 2019, 01:42:21 PM
Depends on how careful you want to be.

There is no way to set the maximum volume of solution, or truly set the volume of a system. However, because water is relatively incompressible and the volume changes relatively little with concentration of solutes (2 percent between pure water and seawater), if you start with  volume of water, it changes relatively little with reaction or changes of pressure.

You can set the total volume of a GAS_PHASE with the -fixed_volume option.

So the following is approximately a 2-liter system that simulates the exposure of a liter of NaCl solution to a 1 L volume of CO2(g) with a pressure of 10 atm. Some of the CO2 dissolves, leaving a gas with a volume of 1 L, but a pressure of 6.3 atm. The volume of the initial NaCl solution is calculated to be 1.022 L (which you could adjust to 1 L with MIX and a fraction of 1/1.022), whereas the volume of the CO2-equilibrated solution is 1.027.

Code: [Select]
SOLUTION
-units mol/kgw
Na 1
Cl 1
END
GAS_PHASE 1
-Fixed_volume 1
CO2(g) 10
END
USE solution 1
USE gas_phase 1
END
Title: Re: Fixed solution volume
Post by: paznativ on August 29, 2019, 06:44:44 PM
Dear Dr. Parkhurst, thank you for the quick reply
I will check to see if this solves our problems

thank you again
Paz