Which of the following redox reactions do you expect to occur spontaneously in the forward direction? check all that apply.
a. pb(s)+mn2+(aq)→pb2+(aq)+mn(s)
b. fe2+(aq)+zn(s)→fe(s)+zn2+(aq)
c. cr(s)+3ag+(aq)→cr3+(aq)+3ag(s)
d. cd2+(aq)+co(s)→co2+(aq)+cd(s)

The redox reactions that occur spontaneously are reaction b and reaction c.

Explanation:

For the reaction to be spontaneous, the Gibbs free energy of the reaction must come out to be negative.

Relationship between standard Gibbs free energy and standard electrode potential follows:

For a reaction to be spontaneous, the standard electrode potential must be positive.

To calculate the of the reaction, we use the equation:

      .......(1)

Substance getting oxidized always act as anode and the one getting reduced always act as cathode.

The given chemical equation follows:

Oxidation half reaction:  

Reduction half reaction:  

Putting values in equation 1, we get:

As, the standard electrode potential is coming out to be negative, this means that standard Gibbs free energy will be positive.

Thus, the reaction will be non-spontaneous.

The given chemical equation follows:

Oxidation half reaction:  

Reduction half reaction:  

Putting values in equation 1, we get:

As, the standard electrode potential is coming out to be positive, this means that standard Gibbs free energy will be negative.

Thus, the reaction will be spontaneous.

The given chemical equation follows:

Oxidation half reaction:  

Reduction half reaction:      ( × 3)

Putting values in equation 1, we get:

As, the standard electrode potential is coming out to be positive, this means that standard Gibbs free energy will be negative.

Thus, the reaction will be spontaneous.

The given chemical equation follows:

Oxidation half reaction:  

Reduction half reaction:  

Putting values in equation 1, we get:

As, the standard electrode potential is coming out to be negative, this means that standard Gibbs free energy will be positive.

Thus, the reaction will be non-spontaneous.

Hence, the redox reactions that occur spontaneously are reaction b and reaction c.