n natural groundwater, we may observe dissolved Fe2+ (aq) at very low pO2. As th

Question

n natural groundwater, we may observe dissolved Fe2+ (aq) at very low pO2. As the water rises to the surface, the fugacity of the O2 increases to non-negligible levels. Use the standard reduction potentials below to answer the questions: .02 + 4H+ + 4 e" ? 2H20 : ·Fe3+ + e-? Fe2+ : E. =1.229 V (a) (2 points) Balance the proposed redox half-reactions, then write the full reaction for the oxidation of Fe2+ ions. (b) (1 point) What is the m? (e) (1 point) What is the AG zan given Faradays Constant of 96485 C/mol electrons? (express in units of [kJ]) (d) (1 point) Is the reaction spontaneous or non-spontaneous? (circle one)

Explanation / Answer

Write the first reaction as it is

Reduction reaction

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

E red = 1.229 V

Write the reverse of the second reaction and multiply by 4

Oxidation reaction

4Fe2+ = 4Fe3+ + 4e-

Eox = - 0.77 V

Part a

Full reaction

O2 + 4H+ + 4Fe2+ = 4Fe3+ + 2H2O

Part b

E°rxn = Eox + Ered

= - 0.77 + 1.229

= 0.459 V

Part C

G°rxn = - nFE°rxn

= - 4mol x 96485 C/mol x 0.459 V

= - 177146.46 J

= - 177.146 kJ

Part d

G°rxn < 0

The reaction is spontaneous.

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