Question

For each reaction listed, determine its standard cell potential (in V) at 25°C and whether the reaction is spontaneous at standard conditions.

(a) 2 Au(s) + 3 Zn2+(aq) → 2 Au3+(aq) + 3 Zn(s)

(b) Co²⁺(aq) + Hg(l) → Co(s) + Hg²⁺(aq)

(c) Cu(s) + Fe(NO₃)₃(aq) → CuNO₃(aq) + Fe(NO₃)₂(aq)

(d) Sn(NO₃)₂(aq) + Zn(s) → Sn(s) + Zn(NO₃)₂(aq)

Answer 1

(a) 2 Au(s) + 3 Zn²⁺(aq) → 2 Au³⁺(aq) + 3 Zn(s)

3 Zn²⁺(aq) + 6e -----------> Zn(s) E° (V) = -0.76V ---------------1

2 Au³⁺(aq) + 6e ---------->2Au(s)   E° (V) = +1.40V ----------------2

Subtracting 2 from 1

2 Au(s) + 3 Zn²⁺(aq) → 2 Au³⁺(aq) + 3 Zn(s)

Ecell = Ecathode - Eanode = -0.76 - (1.40) = -2.16V

Since E is negative, this reaction is non spontaneous

b.) Co2+(aq) + Hg(l) → Co(s) + Hg2+(aq)

Cu(s) + Fe(NO3)3(aq) → CuNO3(aq) + Fe(NO3)2(aq)

Co²⁺(aq) + 2e-----------> Co(s)    E° (V) = -0.28V ---------------1

Hg²⁺(aq) + 2e ---------->Hg(l) E° (V) = +0.91V ----------------2

Subtracting 2 from 1

Co2+(aq) + Hg(l) → Co(s) + Hg2+(aq)

Ecell = Ecathode - Eanode = -0.28 - (0.91) = -1.19V

Since E is negative, this reaction is non spontaneous.

c.) Cu(s) + Fe(NO3)3(aq) → CuNO3(aq) + Fe(NO3)2(aq)

Fe³⁺(aq) + e-----------> Fe²⁺(aq)    E° (V) = 0.77V ---------------1

Cu⁺(aq) + e ---------->Cu(s)   E° (V) = -0.159V ----------------2

Subtracting 2 from 1

Cu(s) + Fe(NO3)3(aq) → CuNO3(aq) + Fe(NO3)2(aq)

Ecell = Ecathode - Eanode = 0.77 - (-0.159) = 0.929 V

Since E is positive, this reaction is spontaneous.

d.) Sn(NO3)2(aq) + Zn(s) → Sn(s) + Zn(NO3)2(aq)

Sn²⁺(aq) + 2e-----------> Sn(s)    E° (V) = -0.13V ---------------1

Zn²⁺(aq) + 2e ---------->Zn(s)   E° (V) = -0.7618V ----------------2

Subtracting 2 from 1

Sn(NO3)2(aq) + Zn(s) → Sn(s) + Zn(NO3)2(aq)

Ecell = Ecathode - Eanode = -0.13 - (-0.7618) = 0.6318V

Since E is positive, this reaction is spontaneous.