Calculate ΔG° Given Cell Reaction, Ec+(–Ea)

Question

Use the standard reduction potentials located in the 'Tables' linked above to calculate the standard free energy change in kJ for the reaction:

Ni²+ (aq) + 2Cr²+ (aq) → Ni(s) + 2Cr³+ (aq)

_______kJ

K for this reaction would be _____ than one.

Answer 1

Ni²+ (aq) + 2Cr²⁺ (aq) → Ni(s) + 2Cr³⁺ (aq)

Not sure what table you use, but:

2e+Ni²+ (aq)→ Ni(s) E=-0.26 V

Cr²⁺ (aq) →Cr³⁺ (aq) E= -0.407 V, but this reaction is flipped, so, flip the sign of E

Cr²⁺ (aq) →Cr³⁺ (aq) E=+0.407 V (multiplying by 2 doesn't change E)

Add the E values together after flipping the sign for the Cr one to E=+0.407 V

2e+Ni²+ (aq)→ Ni(s) E=-0.26V

2Cr²⁺ (aq) →2Cr³⁺ (aq) +2e E=+0.407 V

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Ni²+ (aq) + 2Cr²⁺ (aq) → Ni(s) + 2Cr³⁺ (aq) E=+0.147V

Now use the equation:

ΔG=-nFE

n=mol electrons in half reactions

F=96485 c/mol electrons

E=0.147 V = 0.147 J/c

G=(-2)96485(0.147)

G= -28367 J/mol

1000J=1kJ, divide by 1000

G= -28.367 J

K for this reaction would be GREATER than one.

Because:

+E=spontaneous forward

-G=spontaneous forward

K>1= forward reaction favored