Half reaction, Gibbs free energy A technology to convert organic material in was
ID: 1047906 • Letter: H
Question
Half reaction, Gibbs free energy
A technology to convert organic material in wastewater into electricity is the microbial fuel cell (MFC). A microbial fuel cell facilitates an anaerobic environment with organic material (waste). Bacteria that grow on an electrode consume the organic material, and in absence of oxygen, they produce protons and electrons. For example, the consumption of acetic acid by bacteria in a microbial fuel cell can be described as: CH_3COOH (aq) + 2 H_2O (I) rightarrow 2 CO_2 (aq) + 8 H^+ (aq) + 8 e^- Because this reaction creates electrons, this will act as an anode. To use this electricity, a closed circuit is required; so a cathode should be available as well, where the electrons are accepted by another reaction. Usually, this reaction is the reduction of oxygen: O_2 (g) + 4 H^+ (aq) + 4e^rightarrow 2 H_2O (I) For practical reasons (the first reaction should be anaerobic, and the second reaction should have oxygen), a membrane is placed in between the reaction chamber for the bacteria and the reduction of oxygen. That membrane allows ions (such as H^+) to pass, but no oxygen is exchanged. Write down the overall reaction for the oxidation of acetic acid and reduction of oxygen. Assume that the reaction above occurs at standard conditions. Calculate the Gibbs free energy that is released per mole of acetic acid.Explanation / Answer
CH3COOH + 2H2O -----> 2CO2 + 8H+ + 8e- -----1
O2 + 4H+ +4e -----> 2H2O ------2 = Eo = 1.229 V
Reaction 1 + 2*Reaction 2 ===>
CH3COOH+ 2O2 ------> 2CO2 + 2H2O
Overall reaction
CH3COOH+ 2O2 ------> 2CO2 + 2H2O
2] delta G = -nFEo
Eo is cell potential value
n = no of elctrons transferred = 8
F = 96500 C
Eo = 1.229 + [E value of first reaction]
I dont know tha value of E ; if u know substitute in above equation and get the delta G value
delta G = -8*96500(1.229 + E of 1st reaction )
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