Galvanic Cells

A cell is a highly useful device that is used to convert chemical energy to electrical energy and vice-versa. We use cells in our daily life for various purposes. A Galvanic Cell also called Voltic Cell is an electrochemical device that converts electrical energy into chemical energy.  It uses the spontaneous energy of redox reactions to make electrical energy. Let’s learn about Galvanic Cells in detail in this article.

What is a Galvanic Cell?

The devices in which chemical reaction produces electrical energy are called galvanic cells or voltaic cells. In these devices, the Gibbs energy of the spontaneous redox reaction is converted into electrical work that can be used to drive a motor or to power electrical equipment such as heaters, fans, geysers, etc.

These cells are greatly imported because of their many practical applications. An early example of the galvanic cell is the Daniels cell invented by the British chemist John Daniels in 1836.

Daniel’s cell was constructed based on the redox reaction:

Zn(s) + Cu²⁺(aq)+ → Zn²⁺(aq)+ Cu(s)

In these cells, oxidation and reduction reactions occur in autonomous containers called half cells, and the redox reaction is spontaneous. Electrical energy is fathered during similar reactions. General Representation of a Galvanic Cell:

M₂(s)/M₂ⁿ⁺ (aq) || M₂ⁿ⁺(aq)/M₂(s)

Parts of Galvanic Cell

Various parts of the Galvanic Cell include,

• Anode: The electrode at which oxidation occurs is the anode.
• Cathode: The electrode at which reduction occurs is the cathode.
• Salt bridge: It is a tube filled with electrolytes that maintain the neutrality of the Galvanic Cell.
• Half-cells: Two separate beakers where oxidation and reduction occur are called Half-Cell.
• External circuit: It helps to conduct the flow of electrons between electrodes.

Constructions of Galvanic Cell

A galvanic cell is made by combining two electrodes an oxidation electrode and a reductions electrode. Both electrodes individually are called the half cell. The two half-cells are individually filled with different electrolytic solutions which helps in their particular reaction. Both the half cell are connected to each other using a Salt Bridge.

Oxidation occurs at the oxidation electrode which releases the free electrons that accumulate on the electrode and provide a negative potential. The electrode at which oxidation occurs is called the anode.

Reduction occurs at the reduction electrode that generates the positive charge and provides the positive potential. The electrode at which reduction occurs is called the cathode.

Connecting these electrodes initiate the flow of electrons from one electrode to another resulting in a flow of electric current. For a galvanic cell, the anode is negatively charged and the cathode is positively charged.

Principle and Working of Galvanic Cell

The working of the Galvanic Cell is discussed in this article. 

• Electrodes are exposed to the electrolyte at the electrode-electrolyte interface, which generates ions in the electrolyte solution making one metal electrode negatively charged. 
• For the other electrode, the metal ions in the electrolyte solution deposit on the other metal electrode making the electrode positively charged.
• Due to this charge separation, a potential difference is developed between both electrodes. This potential difference is called electrode potential.
• Electrode, where oxidation occurs, is the anode while the electrode where reduction occurs is the cathode.
• Anode is at a negative potential with respect to the solution while the cathode is at a positive potential with respect to the solution.
• Potential difference between these two electrodes is called the potential of a Galvanic cell and is responsible for the flow of electrons in the circuit.

Example of Galvanic Cell

Daniel’s cell is the most common example of a galvanic cell. The galvanic cell converts chemical energy into electrical energy. For a Galvanic Cell Copper Ions are reduced at the cathode and Zinc Ions are oxidized at the anode.

Reactions taking place at the cathode and anode of a Galvanic cell are:

At Anode: Zn → Zn²⁺ + 2e^–

At Cathode: Cu²⁺ + 2e^– → Cu

What is Salt Bridge?

Salt Bridge is a U- shaped tube that contains a concentrated solution of inert electrolytes. Some examples of electrolytes used in the salt bridge are KCl, KNO₃, K₂SO₄, etc. These inert electrolytes do not participate in the cell reaction.

Salt Bridge allows the movement of ions from one solution to the other without mixing two solutions. The salt bridge also helps to maintain the electrical neutrality of the solution in the two half-cells.

Difference between Galvanic Cell and Electrolytic Cell

Galvanic Cells and Electrolytic Cells are both electrochemical cells and the major difference between them is as follows:

Galvanic Cell	Electrolytic Cell
It converts chemical energy into electrical energy.	It converts electrical energy into chemical energy.
The reactions are spontaneous in Galvanic Cell	The reactions are non-spontaneous in Electrolytic Cell.
Both electrodes, cathodes, and anodes are placed in separate beakers	Both electrodes, cathodes, and anodes are placed in the same beaker.
The electrolytes taken in both beakers are different.	Only one electrolyte is taken.
Oxidation takes place at the anode (negative end), and reduction takes place at the cathode (positive end).	Oxidation takes place at the cathode (positive end), and reduction takes place at the anode (negative end).
A salt bridge is used.	No salt bridge is used.
Gibb’s free energy change during the reaction is negative.	Gibb’s free energy change during the reaction is positive.

Read More:

• Electrochemical Cells
• Redox Reactions and Electrode Processes

Solved Examples on Galvanic Cells

Example 1: Calculate Δ_rG^φ for the reaction: 

Mg(s)+Cu²+ (aq) →  Mg² (aq)+Cu(s)

Given E⁰_cell =2.71 V, 1F = 96500 C mol^-1

Solution:

Δ_rG^φ = -nF 
E^o_cell = 2.71 V,
1 F = 96500 C mol^-1, 
n = 2 

Δ_rG^φ = -2×96500 C mol^-1 ×2.71 V

         = -523030 J mol^-1                     (1CV = 1J)

         = -523.080 kJ mol^-1

Example 2: The  ΔG^φ for the Daniell cell has been found to be -212.3 kJ at 25°C. Calculate the equilibrium constant for the cell reaction.

Solution:

ΔG^φ =-RT ln K_c

ΔG^φ = -212.3 kJ = -212300 J, 
T = 298 K

Here 
R=8.314.K^-1 mol^-1

ln(K_c) = 212300 / (8.314 × 298) 
          = 85.69

K_c = 1.64 × 10³⁷

Example 3: What does the negative sign in the expression E^o_Zn²⁺/Zn =-0.76 V mean?

Solution:

It means that zinc is more reactive than hydrogen. When zinc electrode is connected to SHE, zinc will get oxidized and H⁺ will get reduced.

Example 4: A galvanic cell has an electrical potential of 1.1 V. If an opposing potential of 1.1 V is applied to this cell, What will happen to the reactance of the cell and the current flowing in the cell?

Solution:

When the opposing potential becomes equal to the electric potential, the reaction of the cell stops and no current flows through the cell. Thus, no chemical reaction takes place.

FAQs on Galvanic Cells

Question 1: What is a Galvanic cell?

Answer:

An electrochemical cell that converts the chemical energy of redox reactions into electrical energy is called Galvanic Cell or Voltaic Cell.

Question 2: What is the function of a Galvanic cell?

Answer:

Galvanic cell is a device which provides Electric energy using Chemical energy. It uses the spontaneous energy of the redox reaction for providing electric energy.

Question 3: Is Daniel’s cell a Galvanic cell?

Answer:

Yes, Daniel’s is a galvanic cell. It is the most common example of a galvanic cell.

Question 4: How do you make a Galvanic cell?

Answer:

A galvanic cell is made by dipping two electrodes in a glass vessel solution of dilute sulfuric acid. The two electrodes are made of copper and zinc. The cathode is made of Copper and the anode is made of Zinc.

Question 5: What is the need for the salt bridge in a Galvanic cell?

Answer:

Salt bridge helps to maintain the neutrality of the solution and allows the free flow of ions from one-half cell to another half cell.

Question 6: Where does oxidation occur in a Galvanic cell?

Answer:

In a galvanic cell, oxidation occurs at the Anode.

Question 7: Where does reduction occur in a Galvanic cell?

Answer:

In a galvanic cell, reduction occurs at the Cathode.

Question 8: What is the effect of temperature on the galvanic cell?

Answer:

According to the Nernest Equation, the voltage of the galvanic cell decreases with increasing temperature.