Chapter 20, Problem 67A

(a)

Interpretation Introduction

Interpretation:

The spontaneity of the reaction needs to be explained.

$M{n}^{2+}(aq)+2B{r}^{-}(aq)\to Mn(s)+B{r}_2(l)$

Concept introduction:

If the standard reduction potential for the overall redox reaction is positive, then the reaction becomes spontaneous.

Answer to Problem 67A

This reaction is non-spontaneous.

Explanation of Solution

Oxidation Half reaction:

$2B{r}^{-}\to B{r}_2+2e^{-}\text{ E}°\text{=}-2.18$

Reduction Half reaction:

$M{n}^{2+}+2e^{-}\to Mn\text{ E}°\text{=}-1.18$

Overall reduction potential is negative

Since the overall reduction potential is negative, the reaction is non spontaneous.

Interpretation Introduction

(b)

Interpretation:

The spontaneity of the reaction needs to be explained. $2F{e}^{2+}(aq)+S{n}^{2+}(aq)\to 2F{e}^{3+}(aq)+Sn(s)$.

Concept introduction:

If the standard reduction potential for the overall redox reaction is positive, then the reaction becomes spontaneous.

Answer to Problem 67A

This reaction is non-spontaneous.

Explanation of Solution

Oxidation Half reaction:

$M{n}^{2+}+2e^{-}\to Mn\text{ E}°\text{=}-1.18$

$2F{e}^{2+}\to 2F{e}^{3+}+2e^{-}\text{ E}°\text{=}-2.31$

Reduction Half reaction:

$S{n}^{2+}+2e^{-}\to Sn\text{ E}°\text{=}-0.14$

Overall reduction potential:negative

Since the overall reduction potential is negative, the reaction is non spontaneous.

(c)

Interpretation Introduction

Interpretation: Interpretation: The spontaneity of the reaction needs to be explained.

$N{i}^{2+}(aq)+Mg(s)\to Ni(s)+M{g}^{2+}(aq)$.

Concept introduction:

If the standard reduction potential for the overall redox reaction is

positive, then the reaction becomes spontaneous.

Answer to Problem 67A

This reaction is spontaneous.

Explanation of Solution

Oxidation Half reaction:

$M{n}^{2+}+2e^{-}\to Mn\text{ E}°\text{=}-1.18$

$Mg\to M{g}^{2+}+2e^{-}\text{ E}°\text{=2}\text{.37}$

Reduction Half reaction:

$N{i}^{2+}+2e^{-}\to Ni\text{ E}°\text{=}-0.23$

Overall reduction potential:positive

Since the overall reduction potential is positive, the reaction is spontaneous.

(d)

Interpretation Introduction

Interpretation:

The spontaneity of the reaction needs to be explained. $P{b}^{2+}(aq)+2C{u}^{+}(aq)\to Pb(s)+2C{u}^{2+}(aq)$.

Concept introduction:

If the standard reduction potential for the overall redox reaction is positive, then the reaction becomes spontaneous.

Answer to Problem 67A

This reaction is non spontaneous.

Explanation of Solution

Oxidation Half reaction:

$M{n}^{2+}+2e^{-}\to Mn\text{ E}°\text{=}-1.18$

$2C{u}^{+}\to 2C{u}^{2+}+2e^{-}\text{ E}°\text{=-0}\text{.32}$

Reduction Half reaction:

$P{b}^{2+}+2e^{-}\to Pb\text{ E}°\text{=}-0.13$

Overall reduction potential:negative

Since the overall reduction potential is negative, the reaction isnon spontaneous.