(a) Construct a half reaction for oxidation of acetate into carbon dioxide. (b)

Question

(a) Construct a half reaction for oxidation of acetate into carbon dioxide.

(b) Construct a half reaction for reduction of hydrogen ion into hydrogen.

(c) Construct a balanced an oxidation and reduction reaction by combining the two

half reactions above.

(d) Calculate the standard Gibbs free energy change (?G0) of the balanced equation.

(e) Calculate the standard electrode potentials (E0) for the two half reactions.

(f) Propose the conditions to make the reaction being spontaneous

Acetate (CH3COO') can be oxidized into carbon dioxide (C02(aq)) and hydrogen ion (H+) is reduced to hydrogen (H2(aq)) by microorganisms in anaerobic condition. Thermodynamic Constants for Species of Importance in Water Chemistry Values of Constants Metric Equivalents of Standard Units

Explanation / Answer

a) the half reaction for oxidation is

CH3C00- ------> 2C02 + 3H+ + 4e-

b) the half reaction for reduction is

2H+ + 2e- ----> H2

c) the combined reaction is

CH3C00- + H+ -----> 2C02 + 2H2

d) we know that

dG rxn = dGo products - dGo reactants

so

dGo rxn = 2 x dGo C02 + 2 x dGo H2 - dGo H+ - dGo CH3C00-

dGo rxn = -2 x 94.26 - 2 x 0 - 0 + 89

dGo rxn = -99.52

so dGo value is -99.52 kJ

e) we know that

dGo = - nFEo

here n is the number of electrons transferred

from the above reaction

n = 4

F= 96493

so - 99.52 x 1000 = - 4 x 96493 x Eo

Eo = 0.2578

so the Eo value is 0.2578 V

f) for the reaction to be spontaneous

dG < 0 and

E cell > 0

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