Question

Which of the following reactions will occur spontaneously as written? What will the Ɛ°_rxn be under standard conditions?

a) Ni(s) + Zn⁺² (aq)→Ni⁺² (aq) + Zn(s)

b) Al(s) + 3 Ag⁺(aq)→3 Al⁺³(aq) + Ag(s)

c) Fe(s) + Mn⁺² (aq)→Fe⁺² (aq) +Mn(s)

d) 2 Al(s) + 3 Pb⁺² (aq)→2Al⁺³(aq) + 3 Pb(s)

Answer 1

a)
Eo (Ni2+|Ni) = -0.25 V
Eo (Zn2+|Zn) = -0.76 V

Eo is more for Ni, so Ni will be reduced

In given reaction Ni is getting oxidised

So, it is not spontaneous

EO =-0.25 + 0.76 = 0.51 V

b)
Eo (Al3+|Al) = -1.7 V
Eo (Ag+|Ag) = 0.8 V

Eo is more for Ag, so Ag will be reduced

In given reaction Ag is getting reduced

So, it is spontaneous

Eo = 0.8 +1.7 = 2.5 V

c)
Eo (Fe2+|Fe) = -0.44 V
Eo (Mn2+|Mn) = -1.2 V

Eo is more for Fe so Fe will be reduced

In given reaction Fe is getting oxidised

So, it is not spontaneous

EO = -0.44 + 1.2 = 0.8 V

d)

Eo (Al3+|Al) = -1.7 V
Eo (Pb2+|Pb) = -0.13 V

Eo is more for Pb so Pb will be reduced

In given reaction Pb is getting reduced

So, it is spontaneous

Eo = -0.13 + 1.7 = 1.6 V