A lead acid battery (ie, the battery in your car), when charged, contains electr

Question

A lead acid battery (ie, the battery in your car), when charged, contains electrodes of solid lead (Pb) and lead dioxide (PbO2) immersed in a solution of sulfuric acid. The equilibrium potentials for the two half reactions (both written in direction of reductions) are given below.

a) Calculate the cell potential for a single cell lead acid battery.   (note your car battery likely contains 6 cells in parallel, giving a battery voltage 6 x single cell voltage).

PbSO4(s) + 2e- Pb(s) + SO42-(aq)                   E0 = -0.356 V

PbO2(s) + SO42-(aq) + 4H+(aq) + 2e- PbSO4(s) + 2H2O(aq)   E0 = 1.685 V   

b) using your calculated cell potential, determine the Gibb’s free energy change (in units of kJ/mol) for the overall discharge reaction

Pb(s) + PbO2(s) + 2 H2SO4(aq) 2PbSO4(2) + 2 H2O(aq)

Explanation / Answer

most negative will reduce so

E°cell = Ered - Eox = 1.685 - (-0.356) = 2.041 V

then

for b)

G = -nF*E°cell

G= -2*96500*2.041 = -393913 J/mol

G = -39.91 kJ/mol

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