[e-pH diagram]

I have a few questions about how act2 calculates e-pH diagrams.

 

1- I had a similar question/problem with Fact database before about OH[-] ion reference state?. Does act2 use gas or aqueous state as a reference for OH[-]?. Also what reference state does act2 use for carbonate and bicarbonate?

2- I attached the pourbaix diagram for ethanol with this message. However, I could not get the same diagram when I use the "fact" database. Am I missing something about the activity of ionic species? I make my calculations using excel but I use 1 for activity of all ionic, gas and liquid species. In attached file I have E vs A+B*pH equations and they differ a little from act2 results.

3- I am trying to calculate E-pH diagram for ethanol, methane, CO2, HCO3[-], CO3[-2] etc. ? I cannot get the equilibrium between ethanol methane and the other 3 at the same time? what is the problem? I used the organic materials database but I could not get that. I had to suppress carbon from database but when I have both CH4 and C2H5OH the diagram does not show ethanol. When I suppress CH4 then it shows ethanol. Does that mean there is no equilibrium between ethanol and methane at all? I need help with that. My diagram is attached to this e-mail. I appreciate any help or comments.

 

best wishes,

 

Dr. Muhsin IDER

Usak University

 

 

ethanol pourbaix.xlsx

[ethanol eh-ph diagram help]

Hello Brian,

 

Thanks for your help. I was able to plot E=pH diagram involving HCO3-, CH4. CO3-- and CO2. I have another problem with reading and constructing the data. My purpose is actually to see all the reactions in the same E-pH diagram if possible. By doing that I want to get a better understanding of ethanol decomposition mechanisms with respect to E and pH. I actually calculated all the reaction Gibbs energies given in the table.

​The most favorable reaction in terms of Gibbs energy is

C₂H₅OH(l) + 4OH^[-](aq) D CH₄(g) + CO₂(g) + 3H₂O(l) +4e^-

I can not get this equilibrium line with the module. Am I doing something wrong? Is it metastable?

 

​the other most favorable reactions are as follows:

 

1- C₂H₅OH(l) + H₂O(l) + 4KOH(s) D 6H₂(g) + 2K₂CO₃(s)

2- C₂H₅OH(l) + 2 OH^[-](aq) D 2CO₂(g) + 4H₂(g) +2e^-

3- C₂H₅OH(l)+ 2OH^[-](aq) D CH₄(g)+ CO₂(g)+ H₂O(l) + H₂(g)+2 e^-

My problem is how I can show the equilibrium line between ethanol and CH4, CO2, H2 together. For example the reaction number 3 above. How can I represent the equilibrium line in he diagram for reaction 3. I mean according to E=pH diagram the right side of the equilibrium line must be the zone where CH4, CO2, H2 are stable and the other side must be ethanol. Similarly for number 2 above. I can not get ethanol equilibrium with CO2 and H2 together.

​

Thanks for any help

diagrams are in attached file.

best wishes.

 

 

Muhsin IDER

diagrams.docx

[ethanol eh-ph diagram help]

I need to check e-ph diagram for ethanol. I calculated many reactions in excel myself and I want to check it with the software. But I dont know how to use the software effectively. I guess it is becuse I am new with the software. I actually calculated many reactions involving C2H5OH(l), CH4(gas), CO2(gas), H2(gas), O2(gas), CO3[-2][aq], HCO3-[aq], H+ and OH-. Can I obtain e-pH diagram of ethanol and also methanol with all those ionic species.where to start. I appreciate any help. SOme of the reactions are as follows;

 

25 ºC and 1 atm

E⁰(V)= -DG⁰/nF

DG⁰_rx,298.15 (J/[mol)

1. 6H₂(g) + 2HCO₃^[-] (aq) D C₂H₅OH(l) + 3H₂O(l) + 2OH^[-](aq)

 

 

 

-27267, -29455 Ref[2]

2. 6H₂(g) + 2CO₃^[-2] (aq) DC₂H₅OH(l) + H₂O(l) + 4OH^[-](aq)

 

 

14704, 12426 Ref[2]

3. 2H₂(g) + CO₃^[-2] (aq) + CH₄(g) D C₂H₅OH(l) + 2OH^[-](aq)

 

89365

4. CH₄(g) + CO₂(g) + 3/2H₂(g) + e^-D C₂H₅OH(l) + OH^[-] (aq)

-1.1734

113216

5. CH₄(g) + CO₂(g)+ 3H₂O(l) +4e^-D C₂H₅OH(l) + 4OH^[-](aq)

-0.9146

 

352982

6. CH₄(g) + CO₂(g) + 2H₂(g) + 1/2O₂(g) + 2e^- D C₂H₅OH(l) + 2OH^[-](aq)

0.2283

-44055

7. CO₂(g)+ 1/2O₂(g) + 2e^-D CO₃^[-2] (aq)

0.6914

-133420

8. CO₂(g)+ 3H₂(g) + 2e^-D CH₄(g) + 2OH^[-](aq)

-0.1508

29090.445847686129100

9. 2CO₂(g) + 4H₂(g) + 2e^-D C₂H₅OH(l) + 2 OH^[-](aq)

-0.7374

142297

10. 2CH₄(g) + 1.5O₂(g) + 2e^- D C₂H₅OH(l) + 2OH^[-] (aq)

2.009

-387678

11. CH₄(g) + CO₂(g) + H₂O(l) + H₂(g) + 2e^- D C₂H₅OH(l) + 2OH^[-](aq)

-1.0009

 

193144

12. CO₂(g) + CH₄(g) + 3H₂(g) + 3/2O₂(g) + 4e^-D C₂H₅OH(l) + 4OH^[-](aq)

0.9291

-358578

13. 2CO₃^[-2] (aq) + 16H⁺ + 12e^-D C₂H₅OH(l) + H₂O(l)

0.1977

-305244