7. The way we createhydrogen gas is from steam reforming, which is thisreaction:

Question

7. The way we createhydrogen gas is from steam reforming, which is thisreaction:

CH4(g)+ H2O(g) CO(g) + 3 H2(g)

(note: we gethydrogen from gasoline, essentially)

If Icalculate G° atSTP, I know that it is positive and thus the reaction will notwork.

UsingKirchoff’s Law, at what temperature does the reaction becomefavorable at

standard pressure?The data table below has all the necessary information:

Material S°(J/K/mol) fG° (kJ/mol) fH° (kJ/mol) C°p,m(J/K/mol)

CO(g) 197.67 -137.17 -110.5329.14

CH4(g)186.26 -50.72 -74.81 35.31

H2O(g)188.83 -228.57 -241.82 33.58

H2(g)130.68 0.0 0.0 28.82

Assume that the heatcapacities are pressure independent, and don’t worry aboutthe per

molar thing, you canjust find everything as a per molar quantity.

(Hint: The reactionwill become favorable once G(T2)=0 J/mol, where T2 is the answer

your looking for.Isn’t G(T2)=H(T2)- T2×S(T2)? Isn’t the answer ~880 K whenyou

Explanation / Answer

Let's look at what G equals: G=H - TS G = G° + RT lnQ where Q = [gas]low conc./ [gas]high conc.
so Qin this case would be: 2 / 4 (mols of gas in reactant = low / molsof gas in product = high)
fG°for all the reactants and products. So use them tofind G° of the reaction and then inturn  G (note that is differentfrom G°) or you could also use the enthalpies andentropies of standard formation, also given.
Set G = 0 (since when it goes negative, it becomesspontaneous) Solvefor T!
Don'tforget your assumptions: - Areyou assuming they're all ideal gases? - Areyou ignoring the vibrational contributions to Cp? - Areyou assuming that bond energies are additive?

  
fG°for all the reactants and products. So use them tofind G° of the reaction and then inturn  G (note that is differentfrom G°) or you could also use the enthalpies andentropies of standard formation, also given.
Set G = 0 (since when it goes negative, it becomesspontaneous) Solvefor T!
Don'tforget your assumptions: - Areyou assuming they're all ideal gases? - Areyou ignoring the vibrational contributions to Cp? - Areyou assuming that bond energies are additive?

  
  

Related Questions

Navigate

• Browse (All)
• Browse 7
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.