One way methane is produced is via reduction of carbon dioxide, which serves as

Question

One way methane is produced is via reduction of carbon dioxide, which serves as electron acceptor, with molecular hydrogen, which serves as electron donor.

A) Write a balanced stoichiometric equation for the above stated process and calculate the reaction standard free-energy change (Go') based on free energies of formation (Gfo).

B) When the pressure of the carbon dioxide and methane is 0.80 atm and 0.65 atm, respectively, calculate the minimum molecular hydrogen (H2) concentration (atm) required in order the actual free-energy change (G) to be at least equal to the above calculated standard free-energy change (Go').

C) For the same process, i.e., methane production via CO2 reduction with H2, calculate the reaction standard free-energy change (Go') based on reduction potentials.

Explanation / Answer

A) Balanced equation would be,

CO2(g) + 4H2(g) ---> CH4(g) + 2H2O(g)

dGo = dGo(products) - dGo(reactants)

        = (-50.8 + 2 x -228.61) - (-394.39)

        = -113.63 kJ/mol

B) dG = -RTlnKeq

113.63 = 8.314 x 298 x ln[(0.65)/(0.80)(x^4)

x = 0.94 atm

So the minimum molecular H2 pressure required would be 0.94 atm

C) Standard values feed in the same way as above to calculate free energy using,

dGo = -nFEcell

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