Chapter 21.1, Problem 2LC

Interpretation Introduction

Interpretation: The source of electrical energy produced in a voltaic cell needs to be described.

Concept Introduction: In a voltaic cell, oxidation takes place at the anode and reduction takes place at the cathode. In oxidation, electrons are released and in reduction, electrons are added to the reactant. The oxidation state of the reactant increases during oxidation and decreases during reduction.

Explanation of Solution

In a voltaic cell, a redox reaction takes place. The energy released during this spontaneous redox reaction is used to generate electricity.

Here, in a redox reaction, both oxidation and reduction reactions occur. Here, two half-reactions occur where in one reaction oxidation takes place and in the other reaction, reduction takes place. The sum of these two-half reactions gives the overall reaction for the process.

In oxidation, the loss of electrons takes place by an element, and its oxidation state increases. For example, the oxidation of Ca can be represented as follows:

  $\text{Ca}\left(s\right)\to {\text{Ca}}^{2+}\left(aq\right)+2e$

Similarly in reduction, the gain of electrons takes place by an element. Here, the oxidation state of the element decreases. For example, the reduction of Cu can be represented as follows:

  ${\text{Cu}}^{2+}\left(aq\right)+2e\to \text{Cu}\left(s\right)$

The sum of these two half-reactions gives the overall cell reaction which is spontaneous. The energy released during this spontaneous redox reaction is used to generate electricity.