Chapter 7, Problem 7Q

(a)

Interpretation Introduction

Interpretation:

The given lithium-iodide cell reaction the oxidation half-reaction and reduction half-reaction have to be explained.

Concept introduction:

A galvanic cell is an electrochemical cell. Electrochemical cell is a device capable of converting chemical energy into electrical energy or induces chemical energy by electrical energy. In the galvanic cell spontaneous redox reaction takes place. Redox reaction means the reaction in which the oxidation state of the atoms changes due to the occurrence of both reduction and its complementary oxidation reactions. The element under oxidation reaction loses electron whereas the element in the reduction gains electron.

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.

Explanation of Solution

Oxidation half-reaction:

The lithium $Li$ is oxidized to $L{i}^{+}$ it is oxidation reaction.

  $Li(s)\underset{}{\to }L{i}^{+}+e^{-}$

This reaction is oxidation half reaction, because the reactant lithium metal $(Li)$ is lost one electron and changed into lithium ion. Therefore, the given cell reaction is undergoes for oxidation half-reaction.

Reduction half-reaction:

$I_2(s)+2e^{-}\underset{}{\to }2I^{-}$

This reaction is a reduction half reaction, because the two electrons are on the reactants side $(I_2)$, then the reactant is gaining these two electrons. So, this is a reduction half-reaction.

(b)

Interpretation Introduction

Interpretation:

The lithium iodide overall cell reaction has to be written.

Concept introduction:

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.

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

Oxidation: If electrons are moved from a species during a chemical reaction. The species whose electrons are removed is said to be oxidized.

Reduction: If electrons are gained to a species during a chemical reaction. The species which gets electrons are said to be reduced.

Explanation of Solution

The galvanic cell produces energy through the transfer of electrons from one substance to another. In order to represent the electron transfer process, the overall chemical reaction can be divided into two parts as two half reaction.

One of the half reaction, named as oxidation reaction in which chemical species loses electrons.

Consider the given reaction:

  $\begin{array}{l}2Li(s)\underset{}{\to }2L{i}^{+}+\cancel{2e^{-}}---Oxidationhalfreaction\\ I_2(s)+\cancel{2e^{-}}\underset{}{\to }2I^{-}----\mathrm{Re}ductionhalf-reaction\\ ---------------\\ 2L{i}^{+}+2I^{-}\underset{}{\to }2LiI(s)---Overallreaction\\ ---------------\end{array}$

Above reaction is a oxidation half reaction, the lithium $(Li)$ is lost two electrons to $(L{i}^{2+})$ it is a oxidation half-reaction.

Further the iodine undergoes for reduction half reaction, the two electrons are on the reactants side $(I_2)$, then the reactant is gaining electrons, and this is a reduction half-reaction.

Further combine the two half-reaction to obtain the overall balanced equation becomes a lithium iodide $LiI$

(c)

Interpretation Introduction

Interpretation:

The following cell reaction that occurs at the anode and at the cathode has to be identified.

Concept introduction:

A redox reaction is a chemical reaction where both oxidation and reduction occur simultaneously. In a redox reaction, one of the reactants is oxidized, while the other reactant is reduced at the same time. It can be represented as two half-reactions with the number of transferred electrons. They are as follows:

• • Oxidation half-reaction.
• • Reduction half-reaction.

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.

Explanation of Solution

Oxidation half-reaction:

The lithium $Li$ is oxidized to $L{i}^{+}$ it is oxidation reaction.

  $Li(s)\underset{}{\to }L{i}^{+}+e^{-}$

This reaction is oxidation half reaction, because the reactant lithium metal $(Li)$ is lost one electron and changed into lithium ion. Therefore, this reaction occurs at the anode.

Reduction half-reaction:

$I_2(s)+2e^{-}\underset{}{\to }2I^{-}$

This reaction is a reduction half reaction, because the two electrons are on the reactants side $(I_2)$, then the reactant is gaining these two electrons. So, this reaction occurs at the cathode.