Problem 66 - Chemistry: An Atoms-Focused Approach

Question

The anode in an electrochemical cell is defined as the electrode where oxidation takes place. Why is the anode in an electrolytic cell connected to the positive \((+)\) terminal of an external supply, whereas the anode in a voltaic cell battery is connected to the negative \((-)\) terminal?

Step-by-Step Solution

Answer

Answer: In an electrolytic cell, the anode is connected to the positive terminal, while in a voltaic cell, the anode is connected to the negative terminal. This is because the positive terminal in an electrolytic cell attracts anions for oxidation, forcing the non-spontaneous redox reaction to occur. In a voltaic cell, the spontaneous oxidation that takes place at the anode produces electrons that flow toward the negative terminal and then to the cathode for reduction.

Step 1: Understand the Electrodes

In an electrochemical cell, there are two electrodes: the anode and the cathode. The anode is defined as the electrode where oxidation takes place, and the cathode is defined as the electrode where reduction occurs.

Step 2: Define Electrolytic and Voltaic Cells

Electrochemical cells can be divided into two types: 1. Electrolytic Cells: These cells use electrical energy from an external supply to force a non-spontaneous redox (reduction-oxidation) reaction to occur. 2. Voltaic Cells (also called Galvanic Cells): In these cells, a spontaneous redox reaction generates electrical energy that can be harnessed for use.

Step 3: Anode Connection in Electrolytic Cell

In an electrolytic cell, the anode is connected to the positive \((+)\) terminal of an external supply. This is because the positive terminal attracts negatively charged species (anions) towards it, where oxidation occurs. The external voltage supplied in this case is higher than the potential of the cell, causing the non-spontaneous reaction to be driven forward.

Step 4: Anode Connection in Voltaic Cell

In a voltaic cell, the anode is connected to the negative \((-)\) terminal. This is because the electrons produced by the spontaneous oxidation occurring at the anode flow through the wire towards the negative terminal. The electrons then transfer to the cathode (connected to the positive terminal), where the reduction occurs.

Step 5: Summary of the Anode Connections

The anode in an electrolytic cell is connected to the positive \((+)\) terminal of an external supply because it facilitates the driving of the non-spontaneous redox reaction by attracting anions for oxidation. In a voltaic cell, the anode is connected to the negative \((-)\) terminal because the spontaneous oxidation that occurs at the anode produces electrons that flow toward the negative terminal (and then to the cathode).