Chapter 8, Problem 31Q

The company ZPower is promoting its silver–zinc batteries as replacements for lithium-ion batteries in laptops and cell phones.

1. a. What advantages do silver–zinc batteries have over current Li-ion batteries?
2. b. Write the oxidation and reduction half-reactions for ZPower’s proposed battery using this overall cell equation as a guide. Indicate which reactant gets oxidized and which gets reduced.

$\text{Zn}+{\text{Ag}}_2\text{O}\to \text{ZnO}+2\text{Ag}$

Interpretation Introduction

Interpretation:

The advantages of Silver-zinc batteries over lithium-ion batteries have to be explained.

Concept introduction:

In any electrochemical reaction, an electron goes from one substance to another substance driven by the oxidation-reduction reaction. Electrochemical cells have two conducting electrodes, called the anode and cathode. The anode is defined as the electrode where oxidation occurs. The cathode is the electrode where reduction takes place. Standard electrode potential $\left(E^{°}cell\right)$ can be calculated for both oxidation and reduction reactions. A positive value of $\left(E^{°}cell\right)$ indicates that the reaction proceeds spontaneously in the forward direction whereas, a negative value of $\left(E^{°}cell\right)$ indicates that the reaction proceeds spontaneously in backward direction. The standard cell potential expression is written as follows,

$E^{°}cell=E^{°}{}_{cathode}+E^{°}{}_{anode}$

Explanation of Solution

Lithium-ion battery is best choice than the Silver-zinc battery, because ZPower is taking the leading role in launching the next generation of rechargeable, silver-zinc battery for microbattery applications. This advantage battery offers superior performance over traditional technologies delivering $40\%$ more energy than lithium-ion and 2 or 3 times the energy of nickel metal hydride.

Further the ZPower batteries also offer a green solution since $95\%$ of the battery elements can be recycled and rushed.      

The mercury-free design is inherently safe due to it is water based electrolyte which is not susceptible to thermal runway.

Interpretation Introduction

Interpretation:

The given overall cell equation which is undergoes for oxidation and reduction reaction has to be identified.

Concept introduction:

Oxidation half-reaction: The oxidation half-reaction is the part of a redox reaction that shows only for the oxidized species with the transferred electrons and its oxidation state increases with the loss of electrons.

Reduction half-reaction: The reduction half-reaction is also the part of a redox reaction (the counter part of oxidation half-reaction) that shows only for the reduced species with the transferred electrons and its oxidation state decreases with the gain of electrons.

Overall reaction: It is combining of two molecules in together.

Example: Hydrogen and oxygen to form water, the cell provides a drinking water supply for the astronauts as well as the electricity for the lights, computer, etc., on the board.

$\begin{array}{l}2H_2(g)+2O{H}^{-}(aq)\underset{}{\to }2H_{2}O+2e^{-}---Anodereaction\\ O_2(g)+2H_{2}O+4e^{-}\underset{}{\to }4O{H}^{-}(aq)---cathodereaction\\ --------------------\\ 2H_2(g)+O_2(g)\underset{}{\to }2H_{2}O(l)---overallreaction\\ --------------------\end{array}$ 

Explanation of Solution

Given overall reaction is,

$Zn+A{g}_{2}O\underset{}{\to }ZnO+Ag$

Solve the oxidation half-reaction:

The given overall equation $Zn$ is undergoes for oxidation reaction.

  $\text{Zn(s)}\stackrel{}{\to }{\text{Zn}}^{\text{2+}}\text{(aq)}\text{+}{\text{2e}}^{-}$

This reaction is oxidation half reaction, because the reactant zinc $(Zn)$ is lost two electrons and changed into $Z{n}^{2+}$. Therefore, the given cell reaction is undergoes for oxidation half-reaction.

Solve the Reduction half-reaction:

The given overall equation $Ag$ is undergoes for reduction reaction. $Zn+A{g}_{2}O\underset{}{\to }ZnO+Ag$

  $2A{g}^{2+}(aq)+2e^{-}\underset{}{\to }2Ag(s)$

This reaction is a reduction half reaction, because the two electrons are on the reactants side, then the reactant $(Ag)$ is gaining these two electrons. So, this is a reduction reaction.