Chapter 21.2, Problem 16LC

Interpretation Introduction

Interpretation: The cell potential values indicating a spontaneous reaction and a non-spontaneous reaction need to be explained.

Concept Introduction: The relation between change in Gibbs free energy and cell potential is as follows:

  $\Delta G=-nFE$

Here, n is the number of electrons transferred in the reaction and F is Faraday’s constant.

Explanation of Solution

In an electrochemical cell, a redox reaction takes place. In a redox reaction, oxidation and reduction take place simultaneously. There are two electrodes; anode and cathode. Oxidation occurs at the anode and reduction at the cathode.

The cell potential of an electrochemical cell is related to Gibbs free energy as follows:

  $\Delta G=-nFE$

Here, $\Delta G<0$ for spontaneous reactions and $\Delta G<0$ for non-spontaneous reactions.

For the value of $\Delta G$ to be negative or less than zero, the value of E or cell potential must be positive. Similarly, for the value of $\Delta G$ to be positive or more than zero, the value of E or cell potential must be negative.

Therefore, the cell potential values must be positive for a spontaneous reaction and they must be negative for a non-spontaneous reaction.