Cars of the future may make use of hydrogen powered fuel cells (H_2 powered batt

Question

Cars of the future may make use of hydrogen powered fuel cells (H_2 powered batteries). Two possible reactions to consider regarding hydrogen powered fuel cells are: O_2 (g) + 2 H_2O (I) + 4e^- doubleheadarrow 4 OH^- (aq) E degree = 0.400 V 2 H^+(aq) + 2 e^- doubleheadarrow 2e^- doubleheadarrow E degree = 0.000 V What would be the voltage (E) of a fuel cell under the following conditions? Assume that the temperature is 25 degree C. H_2 gas pressure = 1 bar, [H^+] = 0.00100 M, O_2 gas pressure = 1 bar, [OH^-] = 0.0100 M 0.518 V 0.695 V 0.400 V -0.177 V

Explanation / Answer

E° = Ered - Eox = 0.4-0 = 0.4 V

O2 + 2H2O + 4e- = 4OH-

2H2 = 4H+ + 4e-

2H2 + O2 + 2H2O + 4e- = 4OH- +  4H+ + 4e-

2H2 + O2 + 2H2O + 4e- =4OH- +  4H+

2H2 + O2 = 2H2O

Q = [OH-]^4[H+]^4/(P-H2)^2*[P-O2)

Q = (0.01^4)(0.001^4) / (1*1)

Q = 10^-20

E = E° -0.0592/n*log(Q)

E = 0.4 - 0.0592/4*log(10^-20) = 0.696

choose B, 0.695 V

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