Jump to content
Geochemist's Workbench Support Forum

Outputs of results & ATP number in X2t


Recommended Posts



I have two questions.



I have attached the X2t trial file which condition was so simplified. I have found that the values of Aqueous species on the X2t_output are different from the values of the species in fluid gained from the Map View of Xtplot after calculation of ‘Go Initial’.


My Input value of Cl- is 1 mol/L in all nodes.

The value of Cl- on X2t_output.txt is 1.009 mol/L in all nodes.

The value of Cl- on the Map View of Xtplot is 1.0000000385 mol/L in all nodes.


Which value is correct?

I’m afraid that many a small error makes a big difference later.

I guess that the difference between input and initial values is brought from equilibrium calculation under the input values. On the other hand, I have no idea of the difference between the values of X2t_output.txt and the Map View of Xtplot. I think my understanding about output of results is not adequate. Could anyone give me any advice?



When ATP number is input on the microbial kinetics of Reactants pane, is the value (1) the number of proton per 1 molar of substance, (2) the total number of proton included in substance per the reaction, or (3) the total number of proton per the electron acceptor?

For example, in the former reaction of denitrification as below, I assume that the produced ATP number per proton is one.

5*C3H5O3- + 12*NO3- + 2*H+

In this case, which is correct, (1) 5, (2) 25, or (3) 25/12 ?


As with ATP number, how about stoichiometric number χ? If there is any rule to input their values considering molar number, could you tell me that?


Best regards,




Link to comment
Share on other sites

Hi Maki,


The X2t file looks fine. Keep in mind, you've set the total concentration of Cl- in the Initial pane of X2t (also known as a bulk constraint, or the Cl- component). This value, 1 mol/L, is the sum of the various Cl species in solution: Cl- and NaCl(aq). Due to mass balance on the Cl- component, if you look at the concentration of the Cl- and NaCl(aq) species in Xtplot, you'll find that these add up to 1 mol/L.


In the printed output, the 1.009 value you mention is the concentration of just the free Cl- species, but the units are molal, not mol/L. If I look at the concentration of the free Cl- species in molal units in Xtplot, I get the same answer: 1.009 molal. I did not see anywhere a value equal to 1.0000000385.


I'm currently out of the office teaching a short course, but I'll try to answer the rest of your question when I return next week.




Brian Farrell

Aqueous Solutions LLC

Link to comment
Share on other sites

Hi Brian,


Thank you for your reply.



When Edit -> Copy on the Color Map View with Variable type ‘Components in fluid’ and Variable units ‘mol/l’ after calculation is carried out, the values of text table pasted on excel file etc. shows 1.0000000385.


I understand the explanation about the difference between free and bulk.

And I’ll try to calculate the component concentration according to your suggestion.


On the Color Map View with Variable type ‘Components in fluid’, Cl- values were like below.

Variable units

mol/l -> 1

molal -> 1.019

mol/kg -> 0.9621


In the case of Variable type ‘Species concentrations’, they were like below.

mol/l -> 0.9899

molal -> 1.009

mol/kg -> 0.9524


I understand the difference between the case of mol/l and molal by above advice.

However, why is the value in molal different from that in mol/kg?

Doesn’t ‘molal’ represent 'mol/kg' in GWB software?

If I have misunderstanding, could you let me know?


Thank you for your consideration concerning Q2 and second question for Q1.


Best regards,



Link to comment
Share on other sites

Hi Maki,


We're looking into your question regarding copying values pasted into Excel from the color map.


As for your second question, molal concentration refers to moles of solute per kg solvent (water only), whereas moles per kg refers to kg of solution (water plus all dissolved solutes).




Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...