Question

Distinguish between a voltaic cell and an electrolytic cell in terms of the nature of the reaction involved.

Short answer

Voltaic cells involve spontaneous reactions; electrolytic cells require external energy for non-spontaneous reactions.

Step-by-step solution

- Define Voltaic Cell

A voltaic cell, also known as a galvanic cell, converts chemical energy into electrical energy through a spontaneous redox reaction. In a voltaic cell, the oxidation reaction occurs at the anode, and the reduction reaction occurs at the cathode. The electrons flow from the anode to the cathode through an external circuit, generating electric current.

- Define Electrolytic Cell

An electrolytic cell converts electrical energy into chemical energy through a non-spontaneous redox reaction. In an electrolytic cell, an external electric current is supplied to drive the reaction. The oxidation reaction takes place at the anode, and the reduction reaction occurs at the cathode, similar to a voltaic cell. However, in this case, the energy input is necessary for the reaction to proceed.

- Compare the Nature of Reactions

The key difference between a voltaic cell and an electrolytic cell lies in the nature of the reactions involved. In a voltaic cell, the redox reaction is spontaneous, meaning it occurs naturally without needing external energy. Conversely, in an electrolytic cell, the redox reaction is non-spontaneous and requires an external electrical source to initiate and sustain the reaction.

Key concepts

Voltaic Cell

A voltaic cell, also known as a galvanic cell, is a type of electrochemical cell that converts chemical energy into electrical energy. This process occurs through spontaneous redox reactions. In a voltaic cell:

• The oxidation reaction, where electrons are lost, takes place at the anode.
• The reduction reaction, where electrons are gained, occurs at the cathode.

The electrons flow from the anode to the cathode through an external circuit, generating an electric current. This flow of electrons is harnessed as electrical energy, which can be used to power various devices.

Electrolytic Cell

An electrolytic cell is another type of electrochemical cell, but it works differently from a voltaic cell. It converts electrical energy into chemical energy through non-spontaneous redox reactions. Unlike voltaic cells:

• Electrons are supplied by an external electric current.
• Oxidation still happens at the anode, and reduction still occurs at the cathode; however, the process requires electrical energy input.

This external source of electricity drives the reactions that would not naturally occur on their own. Because of this, electrolytic cells are used in processes such as electroplating and electrolysis of water.

Redox Reactions

Redox reactions, short for reduction-oxidation reactions, are chemical processes in which electrons are transferred between substances. These reactions play a crucial role in both voltaic and electrolytic cells.
In these reactions:

• Oxidation is the loss of electrons from a substance.
• Reduction is the gain of electrons by a substance.

Since oxidation and reduction always occur together, they are collectively called redox reactions. This transfer of electrons is the fundamental principle that allows electrochemical cells to convert energy from one form to another.

Spontaneity of Reactions

The spontaneity of reactions is a major factor that differentiates voltaic cells from electrolytic cells.
In a voltaic cell, the redox reactions occur spontaneously. This means:

• The reactions proceed naturally and do not require external energy input.
• This spontaneous reaction releases energy that is then harnessed as electrical power.

Conversely, in an electrolytic cell, the redox reactions are non-spontaneous and need external electrical power to occur. Thus:

• The external current provides the energy necessary for the reactions.
• Without this input, the chemical changes would not take place.

Chemical to Electrical Energy Conversion

One of the significant aspects of electrochemical cells is their ability to convert energy from one form to another. In a voltaic cell, chemical energy is transformed into electrical energy through spontaneous redox reactions. Here’s how it happens:

• Chemical energy stored in substances is released during the oxidation-reduction process.
• This released energy causes electrons to flow through an external circuit, creating an electric current.

In contrast, an electrolytic cell requires electrical energy to induce chemical reactions that would not occur naturally. Therefore, electrochemical cells are essential tools in various applications, from powering everyday electronics to conducting chemical processes in industrial settings.