Electrochemistry: Meaning, Important Terms, Electrolysis and Redox Reaction

Edited By Shivani Poonia | Updated on Jul 02, 2025 07:59 PM IST

Electrochemistry is the branch of chemistry that studies the relationship between electricity and chemical reactions. It involves the movement of electrons between substances, which can be harnessed to drive chemical reactions or generate electrical energy. Electrochemistry includes various key concepts such as Electrochemical Cells, Redox Reactions, Galvanic Cells, Electrolytic Cells, Nernst Equation,

This Story also Contains

Electrochemistry
Electrolysis
Some Solved Examples
Summary

Electrochemistry

Electrochemistry is the branch of science that deals with transforming chemical energy into electrical energy and vice versa or the relationship between electrical and chemical energy produced in a redox reaction.

Galvanic Cell (or Voltanic Cell)
Consider the following redox reaction:

Zn(s)+Cu2+(aq)⟶Cu(s)+Zn2+(aq)

Zn displaces copper ions (Cu2+) from aqueous solution in the above reaction. This reaction can be achieved very easily in practice. Put a Zn rod into a solution of CuSO₄ (containing Cu²⁺ ions). It is observed that the blue color of the CuSO₄ solution disappears after some time. In this situation, Zn loses 2 electrons per atom, and Cu²⁺ ions in the solution accept them. In this manner, cu2+ ions from the solution are deposited in the form of solid Cu and Zn goes into the solution as Zn²⁺ (colorless). The reaction can well be understood in terms of two half-reactions:

Oxidation : Zn(s)⟶Zn2+(aq)+2e−
Reduction: Cu2+(aq)+2e−⟶Cu(s)

We can make the same reaction occur even if the copper ions and zinc rod are not in direct contact. If we put the Cu²⁺ ions and Zn rod in two separate containers connect the two by a conducting metallic wire and introduce an inverted U-shaped instrument (called a salt-bridge). Electrons will still be transferred through the connecting wires. The electrons from the Zn rod travel to Cu²⁺ ions through the connecting wires and the same reaction occurs. This flow of electrons through the wire generates electricity.

Electrolysis

It is a process by which an electric current is passed through a substance to effect a chemical change. A chemical change is when the substance loses or gains an electron (oxidation or reduction). The process is carried out in an electrolytic cell, an apparatus of positive and negative electrodes held apart and dipped into a solution containing positively and negatively charged ions. The substance to be transformed may form the electrode, constitute the solution, or be dissolved in the solution. Electric current enters through the negatively charged electrode (cathode); positively charged components of the solution travel to this electrode, combine with the electrons, and are transformed into neutral elements or molecules. The negatively charged components of the solution travel to the other electrode (anode), give up their electrons and are transformed into neutral elements or molecules. If the substance to be converted is the electrode, the reaction is generally in which the electrode dissolves by giving up electrons.

Some Solved Examples

Example.1

1. Consider the reaction

2Ag⁺+Cd→2Ag+Cd²⁺

The standard potential for

Ag⁺→Ag and Cd²⁺→Cd couples are 0.80 V and -0.40 V respectively Now,

a) Standard potential E0 for the cell is 1.20V

b) Cd electrode is the negative electrode

Which of the following statements is correct?

1)a

2)b

3) (correct)a,b

4)none

Solution E0=Ecathode 0−Eanod 0

=0.80−(−0.04)=1.20 V

The negative electrode is always the electrode that has a lower value of reduction potential

∴Cd is negative electrode

Hence, the answer is the option (3).

Example.2

2. Choose the correct option :

a) During recharging Gibbs's free energy is positive

b) In a concentration cell, the reduction will take place in the cell's compartment where the concentration is higher

c) Photosynthesis is an electrochemical process

1) (correct)a,b,c

2)a,b

3)b,c

4)a

Solution

Gibbs's free energy is positive as the mark is done on the cell during recharging. Le Chatiler's

principle indicates that reaction is more favorable to reaction when concentration is higher

Photosynthesis is an electrochemical process where water/arsenite is used as an electron.
Hence, the answer is the option (1).

Example.3

3. Which of the following statements is correct?

1)Ecell and ΔG of all reactions are both extensive properties

2)Ecell and ΔG of all reactions are both intensive properties

3) (correct)Ecell is an intensive property while ΔG extensive property

4)Ecell is an extensive property while ΔG intensive property

Solution

Ecell is independent of the number of moles and so is intensive

But ΔG=−nFE it depends on n. Hence, it is an extensive property

Hence, the answer is the option (3).

Example.4

4. Given :

(i)C( graphite )+O₂( g)→CO₂( g);ΔrH^⊖=xkJmol−1

( ii )C( graphite )+12O₂( g)→CO2( g)ΔrH^⊖=ykJmol−1

(iii)CO(g)+12O₂( g)→CO₂( g)ΔrH^⊖=zkkmol−1

Based on the above thermochemical equations, find out which one of the following algebraic relationships is correct.

1)y=2z−x

2)x=y−z

3)z=x+y

4) (correct)x=y+z

Solution

Introduction to Electrochemistry -

ELECTROCHEMISTRY
Electrochemistry is the branch of science that deals with transforming chemical energy into electrical energy and vice versa or the relationship between electrical and chemical energy produced in a redox reaction.

Electrolytic Cell
Consider the following redox reaction:

Zn(s)+Cu²⁺(aq)⟶Cu(s)+Zn²⁺(aq)

Zn displaces copper ions (Cu²⁺) from aqueous solution in the above reaction. This reaction can be achieved very easily in practice. Put a Zn rod into a solution of CuSO₄ (containing Cu²⁺ ions). It is observed that the blue color of the CuSO₄ solution disappears after some time. In this situation, Zn loses 2 electrons per atom, and Cu²⁺ ions in the solution accept them. Cu²⁺ ions from the solution in this manner are deposited in the form of solid Cu and Zn goes into the solution as Zn²⁺ (colorless). The reaction can well be understood in terms of two half-reactions:

Oxidation: Zn(s)⟶Zn²⁺(aq)+2e−
Reduction: Cu²⁺(aq)+2e−⟶Cu(s)

Now, we can make the same reaction occur even if the copper ions and zinc rod are not in direct contact. Suppose we put the Cu2+ ions and Zn rod in two separate containers connect the two by a conducting metallic wire and introduce an inverted U-shaped instrument (called a salt-bridge). In that case, electrons will still be transferred through the connecting cables. The electrons from the Zn rod travel to Cu²⁺ ions through the connecting wires and the same reaction occurs.

C(graphite )+O₂(g)→CO₂(g)ΔrH⁰=xKJ/mol−−−(1)

C(graphite )+12O₂(g)→CO₂( g)ΔrH⁰=yKJ/mol−−−−(2)

CO(g)+12O₂( g)→CO₂( g)ΔrH⁰=zKJ/mol−−−−−(3)

(1)=(2)+(3)

X=Y+Z
Therefore,option(4) is correct

Example.5

5. Which of the following statements is incorrect about the electrolytic cell?

1)It converts electrical energy into chemical energy.

2)The non-spontaneous reaction is made spontaneous by the help of electricity.

3) (correct)ΔG<O for the reaction in electrolytic cell

4)ΔG>O for the reaction in electrolytic cell

Solution

In an electrolytic cell, a non-spontaneous reaction is made spontaneous by the help of electrical energy.

∴ΔG>O for the reaction in electrolytic cel

Hence, the answer is the option (3).

Summary

Electrochemistry gives us so many applications such as batteries, electroplating, corrosion, and fuel cells. Batteries: Electrochemical cells that store and release electrical energy. Common types include lead-acid, nickel-cadmium, and lithium-ion batteries. Electroplating: A process that uses electrolysis to deposit a layer of metal onto a surface. It is used for corrosion protection and decorative purposes. Corrosion: The degradation of metals due to electrochemical reactions with their environment.

Frequently Asked Questions (FAQs)

1. What is electrochemistry?

Electrochemistry is the branch of chemistry that studies the relationship between electrical energy and chemical reactions. It involves the transfer of electrons between species, resulting in oxidation-reduction (redox) reactions. Electrochemistry has applications in batteries, fuel cells, corrosion prevention, and electroplating.

2. How does a salt bridge function in a galvanic cell?

A salt bridge in a galvanic cell serves three important functions: 1) It completes the electrical circuit by allowing ions to flow between the half-cells. 2) It maintains electrical neutrality in both half-cells by providing ions to balance charge. 3) It prevents direct mixing of the solutions in the two half-cells.

3. What is the standard hydrogen electrode (SHE) and why is it important?

The standard hydrogen electrode (SHE) is a reference electrode used to measure standard reduction potentials. It consists of hydrogen gas bubbled over a platinum electrode in a 1 M H+ solution. Its importance lies in its use as a universal reference point (assigned a potential of 0.00 V) against which all other electrode potentials are measured.

4. How does concentration affect cell potential in a galvanic cell?

Concentration affects cell potential through the Nernst equation. As the concentration of reactants increases or products decreases, the cell potential increases. Conversely, as the concentration of reactants decreases or products increases, the cell potential decreases. This relationship allows for non-standard conditions to be accounted for in electrochemical calculations.

5. What is a redox reaction?

A redox reaction, short for reduction-oxidation reaction, is a chemical reaction in which electrons are transferred between species. One species loses electrons (oxidation) while another gains electrons (reduction). These reactions are fundamental to many processes in chemistry and biology.

6. What is the difference between electrolytic cells and galvanic cells?

Electrolytic cells use electrical energy to drive a non-spontaneous chemical reaction, while galvanic cells (also called voltaic cells) produce electrical energy from a spontaneous chemical reaction. In electrolytic cells, electricity is consumed; in galvanic cells, electricity is generated.

7. What is an electrolyte?

An electrolyte is a substance that conducts electricity when dissolved in water or molten. It contains ions that can move freely, allowing for the flow of electric current. Common examples include salt solutions, acids, and bases.

8. What is the difference between oxidation and reduction?

Oxidation is the loss of electrons by a species, resulting in an increase in its oxidation number. Reduction is the gain of electrons by a species, resulting in a decrease in its oxidation number. These processes always occur together in redox reactions.

9. How does temperature affect electrochemical reactions?

Temperature affects electrochemical reactions in several ways: 1) It increases the rate of reactions by providing more kinetic energy to the particles. 2) It can change the standard electrode potentials. 3) In galvanic cells, higher temperatures generally increase the voltage output. 4) In electrolytic cells, higher temperatures usually decrease the voltage required for electrolysis.

10. Why don't all solutions conduct electricity?

Not all solutions conduct electricity because they don't all contain mobile ions. For a solution to conduct electricity, it must have free ions that can move and carry charge. Solutions of covalent compounds, like sugar in water, don't conduct electricity because they don't form ions when dissolved.

11. How do lithium-ion batteries work?

Lithium-ion batteries work through the movement of lithium ions between the anode and cathode. During discharge, lithium ions move from the anode (often graphite) to the cathode (often a metal oxide), while electrons flow through the external circuit, providing power. During charging, an external voltage drives the lithium ions back to the anode. The process is called intercalation, where lithium ions are inserted into and removed from the electrode materials without significantly changing their structure.

12. How does an electrochemical gradient differ from a concentration gradient?

An electrochemical gradient combines both concentration and electrical potential differences. It accounts for the tendency of ions to move due to both their concentration difference and the electrical charge difference across a membrane or between solutions. A concentration gradient only considers the difference in concentration of a species between two regions, ignoring any electrical effects. In many biological systems, both components are important for understanding ion movement.

13. How do electrochemical capacitors (supercapacitors) differ from batteries?

Electrochemical capacitors, or supercapacitors, store energy through the physical separation of charges at the electrode-electrolyte interface, rather than through chemical reactions like batteries. Key differences include: 1) Supercapacitors can charge and discharge much faster than batteries. 2) They have a much longer cycle life. 3) They typically have lower energy density but higher power density than batteries. 4) Supercapacitors maintain their capacity better over time and in extreme temperatures.

14. How does the concept of electronegativity relate to redox reactions?

Electronegativity is the ability of an atom to attract electrons in a chemical bond. In redox reactions: 1) The more electronegative element tends to be reduced (gain electrons). 2) The less electronegative element tends to be oxidized (lose electrons). 3) The difference in electronegativity between elements can predict the likelihood and direction of electron transfer in redox reactions. 4) Electronegativity trends in the periodic table can help predict the strength of oxidizing and reducing agents.

15. What is Faraday's First Law of Electrolysis?

Faraday's First Law of Electrolysis states that the mass of a substance produced or consumed at an electrode during electrolysis is directly proportional to the quantity of electricity passed through the electrolyte. This law relates the amount of chemical change to the amount of electrical charge transferred.

16. What is overpotential and why is it important?

Overpotential is the additional potential beyond the thermodynamically determined potential that is required to drive an electrochemical reaction at a certain rate. It's important because it represents energy losses in real electrochemical systems and affects the efficiency of processes like electrolysis and battery operation.

17. How do fuel cells work?

Fuel cells are electrochemical devices that convert chemical energy directly into electrical energy. They consist of two electrodes separated by an electrolyte. Fuel (often hydrogen) is oxidized at the anode, while oxygen is reduced at the cathode. The electrons flow through an external circuit, producing electricity. Unlike batteries, fuel cells can operate continuously as long as fuel and oxidant are supplied.

18. What is the difference between a primary and secondary battery?

A primary battery is designed to be used once and discarded. The electrochemical reactions are not easily reversible, so it cannot be recharged effectively. Examples include alkaline batteries. A secondary battery, also known as a rechargeable battery, can be recharged and used multiple times. The electrochemical reactions are reversible, allowing the battery to be recharged by applying an external voltage. Examples include lithium-ion batteries.

19. How does corrosion relate to electrochemistry?

Corrosion is an electrochemical process where a metal is oxidized by its environment. It involves the flow of electrons from one part of the metal (acting as an anode) to another part (acting as a cathode). Understanding corrosion as an electrochemical process allows for the development of prevention methods, such as cathodic protection or the use of sacrificial anodes.

20. What is the significance of the electrochemical series?

The electrochemical series, also known as the activity series, is a ranking of elements based on their standard reduction potentials. It's significant because it allows prediction of: 1) The direction of redox reactions. 2) The relative strength of oxidizing and reducing agents. 3) The reactivity of metals with acids or water. 4) The feasibility of metal displacement reactions.

21. How does electrolysis differ from spontaneous redox reactions?

Electrolysis is a non-spontaneous process that requires an input of electrical energy to drive chemical reactions. In contrast, spontaneous redox reactions occur naturally and release energy. Electrolysis often involves breaking down compounds (like water into hydrogen and oxygen), while spontaneous redox reactions often involve the formation of more stable compounds.

22. What is the relationship between Gibbs free energy and cell potential?

The relationship between Gibbs free energy (ΔG) and cell potential (E°) is given by the equation: ΔG = -nFE°, where n is the number of electrons transferred and F is Faraday's constant. This relationship shows that a positive cell potential corresponds to a negative Gibbs free energy, indicating a spontaneous reaction. Conversely, a negative cell potential indicates a non-spontaneous reaction.

23. How do concentration cells work?

Concentration cells are galvanic cells where the same chemical species is present at both electrodes, but at different concentrations. The potential difference arises from the tendency of the system to equalize concentrations. Electrons flow from the electrode with the lower concentration to the one with the higher concentration. The potential can be calculated using the Nernst equation.

24. What is the role of the electrolyte in an electrochemical cell?

The electrolyte in an electrochemical cell serves several crucial roles: 1) It provides ions for conducting electricity within the cell. 2) It completes the internal circuit by allowing ion movement between electrodes. 3) It maintains charge balance as the redox reactions proceed. 4) In some cases, it participates directly in the electrode reactions.

25. How does electroplating work?

Electroplating is an electrolytic process used to coat an object with a thin layer of metal. The object to be plated is made the cathode in an electrolytic cell. The anode is made of the plating metal. When current flows, metal ions from the anode (or the electrolyte) are reduced and deposited onto the cathode, forming a coating. The thickness of the coating can be controlled by adjusting the current and time.

26. What is the difference between standard reduction potential and actual cell potential?

Standard reduction potentials are measured under standard conditions (1 M concentration, 1 atm pressure, 25°C). The actual cell potential can differ from the standard potential due to non-standard conditions. Factors affecting actual cell potential include concentration differences (accounted for by the Nernst equation), temperature changes, and pressure differences for reactions involving gases.

27. How do pH changes affect electrochemical reactions?

pH changes can significantly affect electrochemical reactions, especially those involving H+ or OH- ions. In general: 1) For reactions consuming H+, increasing pH (decreasing H+ concentration) will make the reaction more favorable. 2) For reactions producing H+, decreasing pH will make the reaction more favorable. 3) pH changes can alter the standard reduction potentials of half-reactions involving H+ or OH-.

28. What is the principle behind potentiometric titrations?

Potentiometric titrations use the change in electrode potential to determine the endpoint of a titration. As the titrant is added, the potential of an indicator electrode is measured against a reference electrode. The endpoint is identified by a sharp change in potential, which corresponds to the equivalence point of the reaction. This method is particularly useful for reactions where color changes are difficult to observe.

29. How do electrochemical sensors work?

Electrochemical sensors work by generating an electrical signal in response to a chemical reaction. They typically consist of electrodes that interact with the analyte. The interaction can be through various mechanisms: 1) Amperometric sensors measure current generated by oxidation or reduction of the analyte. 2) Potentiometric sensors measure potential changes due to ion accumulation. 3) Conductometric sensors measure changes in electrical conductivity of the solution.

30. What is the difference between galvanic corrosion and uniform corrosion?

Galvanic corrosion occurs when two dissimilar metals are in electrical contact in the presence of an electrolyte. The more active metal acts as the anode and corrodes faster than it would alone. Uniform corrosion, on the other hand, occurs evenly over the entire surface of a metal exposed to a corrosive environment. It doesn't require the presence of a second metal and results in relatively even thinning of the metal.

31. What is the significance of the Butler-Volmer equation in electrochemistry?

The Butler-Volmer equation is a fundamental equation in electrochemical kinetics. It describes the relationship between electrical current and electrode potential, taking into account both the forward and reverse reactions at an electrode. The equation is significant because: 1) It helps understand the factors affecting reaction rates at electrodes. 2) It's used to analyze and model various electrochemical systems. 3) It forms the basis for understanding more complex electrochemical phenomena.

32. What is cyclic voltammetry and why is it useful?

Cyclic voltammetry is an electrochemical technique where the potential of an electrode is cycled between two values while measuring the resulting current. It's useful because: 1) It provides information about redox reactions, including their reversibility. 2) It can determine the formal reduction potential of an analyte. 3) It can be used to study reaction mechanisms and kinetics. 4) It's valuable for characterizing new compounds or materials in electrochemistry.

33. What is the Cottrell equation and what does it describe?

The Cottrell equation describes the current-time relationship in an electrochemical cell following a step change in potential. It shows that the current decays proportionally to the inverse square root of time. This equation is important because: 1) It's used in techniques like chronoamperometry to determine diffusion coefficients. 2) It helps understand mass transport in electrochemical systems. 3) It forms the basis for more complex electroanalytical techniques.

34. What is the double layer in electrochemistry?

The double layer in electrochemistry refers to the structure formed at the interface between an electrode and the electrolyte. It consists of two layers: 1) A compact layer of ions adsorbed directly onto the electrode surface. 2) A diffuse layer of ions extending into the bulk solution. The double layer is important because: 1) It affects the rate of electron transfer at the electrode. 2) It contributes to the capacitance of the electrode. 3) Understanding it is crucial for interpreting many electrochemical phenomena.

35. How do reference electrodes work and why are they important?

Reference electrodes maintain a constant and stable potential regardless of the solution composition. They typically consist of a metal in contact with its sparingly soluble salt and a solution of constant ion concentration. Reference electrodes are important because: 1) They provide a fixed reference point for measuring potentials of other electrodes. 2) They allow for reproducible potential measurements across different experiments. 3) They're essential in three-electrode setups used in many electrochemical studies.

36. What is the Marcus theory of electron transfer?

The Marcus theory, developed by Rudolph Marcus, explains the rates of electron transfer reactions. Key points include: 1) It considers the reorganization of the solvent and changes in bond lengths during electron transfer. 2) It predicts a parabolic relationship between the rate of electron transfer and the driving force of the reaction. 3) It explains the counterintuitive "inverted region" where reaction rates decrease with increasing driving force. This theory is fundamental to understanding many electrochemical and biological electron transfer processes.

37. How do electrochemical impedance spectroscopy (EIS) work?

Electrochemical impedance spectroscopy (EIS) is a technique that measures the impedance of a system over a range of frequencies. It works by applying a small sinusoidal potential perturbation and measuring the resulting current response. EIS is powerful because: 1) It can separate different processes occurring at different rates. 2) It can provide information about electrode kinetics, diffusion processes, and solution resistance. 3) It's non-destructive and can be used to study systems in equilibrium. 4) It's widely used in studying batteries, fuel cells, and corrosion processes.

38. What is the difference between Faradaic and non-Faradaic processes?

Faradaic processes involve the transfer of electrons across the electrode-solution interface, resulting in oxidation or reduction. They obey Faraday's laws of electrolysis. Non-Faradaic processes, on the other hand, don't involve electron transfer. They include phenomena like double layer charging and adsorption/desorption processes. Understanding this difference is crucial because: 1) It affects the interpretation of electrochemical data. 2) It influences the design of electrochemical devices. 3) It's important in separating different contributions to the overall electrochemical response.

39. How do ion-selective electrodes work?

Ion-selective electrodes (ISEs) are membrane electrodes that respond selectively to certain ions in solution. They work by developing a potential across a membrane that's proportional to the logarithm of the activity of the target ion. The membrane contains a specific ionophore that selectively binds the ion of interest. ISEs are important because: 1) They allow for direct measurement of ion activities. 2) They're used in various fields including clinical chemistry, environmental monitoring, and process control. 3) They can measure ions in complex mixtures