Identify which redox reactions occur spontaneously in the forward direction. check all that apply. check all that apply. 2ag+(aq)+ni(s)→2ag(s)+ni2+(aq) ca2+(aq)+zn(s)→ca(s)+zn2+(aq) 2cr(s)+3pb2+(aq)→2cr3+(aq)+3pb(s) fe(s)+mn2+(aq)→fe2+(aq)+mn(s)

You must look up the standard reduction potentials for the half-reactions and then combine them to get the cell potentials for the reaction as written.

A. Ag⁺/Ni

2×[Ag⁺ + e⁻ ⟶ Ag ] 0.7996 V

1×Ni ⟶ Ni²⁺ + 2e⁻] 0.257 V

2Ag⁺ + Ni ⟶ 2Ag + Ni²⁺ 1.057 V

E° > 0. The cell reaction is spontaneous.

B. Ca²⁺/Zn

Ca²⁺ + 2e⁻ ⟶ Ca -2.868 V

Zn ⟶ Zn²⁺ + 2e⁻ 0.7618 V

Ca²⁺ + Zn ⟶ Ca + Zn²⁺ -2.106 V

E° < 0. The cell reaction is not spontaneous.

C. Cr/Pb²⁺

2×[Cr ⟶ Cr³⁺ + 3e⁻] 0.744 V

3×[Pb²⁺ + 2e- ⟶ Pb] -0.1262 V

2Cr + 3Pb²⁺ ⟶ 2Cr³⁺ 0.618 V

E° > 0. The cell reaction is spontaneous.

D. Fe/Mn²⁺

Fe ⟶ Fe²⁺ + 2e- 0.447 V

Mn²⁺ + 2e- ⟶ Mn -1.185 V

Fe + Mn²⁺ ⟶ Fe²⁺+ Mn -0.738 V

E° < 0. The cell reaction is not spontaneous.