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Redox Reactions

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Redox Reactions are oxidation and reduction reactions that happen simultaneously in a chemical reaction and in this, the reactant undergoes a change in its oxidation state. Redox stands for Reduction – Oxidation. Redox reaction is a common term used in both Chemistry and Biology. They are a certain type of chemical reaction in which the substrate’s oxidation states change.

A reduction is a decrease in the oxidation state or a gain in electrons, whereas oxidation is the loss of electrons or an increase in the oxidation state. A redox reaction involves the transfer of electrons between two species. Redox reactions can occur in two ways, by the electron transfer and by the atom transfer of the chemical species involved in a chemical reaction. Redox Reaction is important for class 10 and class 11 students.

In this article, you will read about what is a redox reaction, its definition, types, and examples of redox reactions.

What is a Redox Reaction?

Redox reaction in Chemistry involves the alteration of oxidation states of the atoms. These reactions involve the actual shifting or transfer of electrons of the chemical species involved in the reaction. So, in this reaction, one species loses electrons while the other gains electrons.

Redox reaction can be determined by the change or difference in the oxidation state of two atoms. If there is no change or difference in oxidation number then there is no redox reaction can take place. 

Redox Reaction Definition

A redox reaction, short for reduction-oxidation reaction, is a chemical process in which the oxidation states (or oxidation numbers) of one or more substances involved in the reaction change.

Types of Redox Reactions

There are four different types of redox reactions, that are:

  • Decomposition Reaction
  • Combination Reaction
  • Displacement Reaction
  • Disproportionation Reaction

Decomposition Reaction

A chemical is broken down into distinct components in this type of reaction. It is the inverse reaction of a combination reaction. In a displacement reaction, for example, the atom gets replaced by an atom of another element. 

A chemical equation will be used to depict the chemical reaction. It denotes the transition from reactants to products. The reactant side is represented on the left, and the result of the reaction is represented on the right.

For examples,

2NaH → 2Na + H2

2H2O → 2H2 + O2

There are three types of decomposition reactions:

  1. Thermolysis – Thermolysis is heat-induced decomposition.
  2. Electrolysis is the decomposition of matter caused by electricity.
  3. Photolysis – Photolysis is decomposition due to light.

Combination Reaction

These reactions, which are the inverse of decomposition processes, require the combination of two chemicals to generate a single compound in the form of A + B → AB.

The outcome of a combination reaction between a metal and a nonmetal is an ionic solid. As an example, lithium can react with sulfur to form lithium sulfide. When magnesium burns in the air, its atoms mix with the gas oxygen to form magnesium oxide. The bright flame produced by flares is produced by this unique combination reaction. 

For examples,

H2 + Cl2 → 2HCl

C + O2 → CO2

Displacement Reaction

An atom or an ion of a compound is replaced by an atom or an ion of another element in this type of reaction. It can be represented as X + YZ → XZ + Y. Displacement reactions are further subdivided into metal displacement reactions and non-metal displacement reactions.

  • Metal Displacement: A metal existing in the compound is displaced by another metal in this type of reaction. These types of reactions are used in metallurgical operations to extract pure metals from their ores. As an example,

CuSO4 + Zn → Cu + ZnSO4

  • Non-Metal Displacement: In this type of reaction, we can detect a hydrogen displacement and, on rare occasions, an oxygen displacement.
  • Single Displacement Reaction: A single displacement reaction, also known as a single replacement reaction, is a type of oxidation-reduction chemical reaction in which one ion or element moves out of a molecule, i.e., one element in a compound is replaced by another.
  • Double Displacement Reaction: Double displacement reactions occur when a portion of two ionic compounds is transferred, resulting in the formation of two new components. This is the pattern of a twofold displacement reaction. Ions precipitate and exchange ions in aqueous solutions, resulting in double displacement processes.

Disproportionation Reactions

Disproportionation reactions are those in which a single reactant is oxidized and reduced. The reaction of hydrogen peroxide, when poured over a wound is one real-life example of such a process. At first glance, this may appear to be a simple breakdown reaction, because hydrogen peroxide decomposes to produce oxygen and water. 

For example,

P4 + 3NaOH + 3H2O → 3NaH2PO2 + PH3

Examples of Redox Reactions

Redox Reactions include both oxidation and reduction reactions. Examples of redox reactions are as follows:

Reaction between Iron and Hydrogen Peroxide

In this redox reaction, H2O2 oxidizes Fe+2 into Fe+3 in the presence of an acid. This results in the formation of Hydroxide ions as shown below:

2Fe22+ + H2O2 + 2H+    →    2Fe3+ + 2H2O

  • Oxidation-half reaction is,

Fe2+    →    Fe3+ + e

  • Reduction-half reaction is,

H2O2 + 2e     →     2 OH

Reaction between Hydrogen and Fluorine

Here in this redox reaction, oxidation occurs at hydrogen and reduction takes place at fluorine. So, Hydrogen and fluorine combine to form Hydrogen Fluoride, as shown below:

H2 + F2     →     2HF

  • Oxidation half of the reaction is, 

H2 → 2H+ + 2e

  • Reduction-half of the reaction is,

F2 + 2e     →     2F
 

Oxidation and Reduction Reaction

Oxidation and Reduction reactions are the basis of Redox reactions so to fully understand the concept of redox reactions, let us learn about oxidation and reduction reactions separately.

What is Oxidation Reaction?

When an atom loses electrons oxidation happens, the oxidation reaction is also defined as the addition of an oxygen atom or the removal of a hydrogen atom. Oxidation number of the atom increases in oxidation reaction.

Some examples of oxidation reactions are:

  • CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (l)
  • 2S(s) + O2 (g) → SO2 (g)

What is Reduction Reaction?

When an atom gains electrons reduction happens, the reduction reaction is also defined as the removal of an oxygen atom or the addition of a hydrogen atom. Oxidation number of the atom decreases in reduction reaction.

Some examples of reduction reactions are:

  • 2CH4 (g) + H2 (g) → 2CH6 (g)
  • 2CuCl2 (aq) + H2 (g) → 2CuCl (aq) + 2HCl (aq)

Observing above reactions we can conclude that both oxidation and reduction happens in above reactions. CuCl2 is reduced as electronegative element chlorine is removed from it. While hydrogen is oxidized due to the addition of chlorine, an electronegative element, in the above reaction.

Oxidizing and Reducing Agents

Oxidizing and Reducing agents are defined as,

Oxidizing Agent: Oxidizing agent are substance that gains electrons and is there oxidation number is reduced.

Reducing Agent: Reducing agent are substance that lose electrons and is there oxidation number is increased.

Important Oxidizing Agents

Some Important Oxidizing Agents include 

  • Electronegative elements such as, O3, and X2 (halogens)
  • Oxides of metals and non-metals such as MgO, CuO, CrO3
  • Compounds containing an element in higher oxidized state such as, KMnO4, K2Cr2O7, HNO3

Note: Fluorine is the strongest known oxidizing agent.

Important Reducing Agents

Some Important Reducing Agents include 

  • Metals such as Na, Zn, Fe, Al
  • Hydracids such as HCl, HBr, HI, H2S
  • Metallic hydrides such as NaH, LiH, CaH2
  • Compounds containing elements in lower oxidation state such as FeCl2, FeSO4, SnCl2, Hg2Cl2

Note: Lithium is the strongest reducing agent in the solution, and Cesium is the strongest reducing agent in the absence of water.

Reduction Potential of a Half-Reaction

A redox reaction has two half-reaction and each half reaction has a standard electrode potential. This standard electrode potential equals the voltage produced by the electrochemical cell in which half-reaction is considered as cathode reaction, while standard hydrogen electrode act as anode.

The voltage produced by half-reactions is called their reduction potentials. It is denoted by E°red. For the oxidizing agents stronger than H+ the reduction potential of half reaction is considered to be positive whereas those are weaker than H+ are considered to be negative.

Reduction potentials of some ions include +2.866 V for F2 and -0.763 V for Zn2+.

Identification of Oxidizing and Reducing Agents

Oxidizing and Reducing Agents are identified as,

  • Element which are is in higher oxidation state in a compound behaves as oxidizing agent such as KMnO4, K2Cr2O7, HNO3, H2SO4, HClO4
  • Element which are is in lower oxidation state in a compound behaves as as a reducing agent such as H2S, H2C2O4, FeSO4, SnCl2
  • If high electronegative element is in its highest oxidation state is behaves as oxidizing agent.
  • The compound acts as a reducing agent if a highly electronegative element is in its lowest oxidation state.

Example: Identify the oxidizing agent and reducing agent in the reactions.

Balancing Redox Reaction

There are two ways of balancing the redox reaction. One method is by using the change in oxidation number of oxidizing agent and the reducing agent and the other method is based on dividing the redox reaction into two half reactions-one of reduction and another of oxidation.

Balancing Redox Reaction by Oxidation State Method

This method is based on the fact that the number of electrons gained during the reduction reaction equals the number of electrons lost in oxidation. An example of this is an equation of rusting of iron. The following equation represents rusting of Iron.

4Fe2+ + O2 → 4Fe3+ + 2O2-

Fe2+ is oxidized to Fe3+ Oxidation by gaining 4 electrons (1 by each Fe atom) and two oxygen atoms each losing 2 electrons lead to loss of 4 electrons.

Balancing Redox Reaction by Ion electron Method (Half reaction method)

The steps for balancing redox reaction are mentioned below:

Step 1: Divide the complete reaction into two half-reactions, each called Redox Half Cell. One Redox representing oxidation called Oxidation Half Cell and the other representing reduction is called Reduction Half Cell.

Step 2: First balance elements other than ‘O’ and ‘H’ atoms.

Step 3: In an acidic or neutral medium, balance oxygen atoms by adding H2O molecules and balance Hatoms by adding H+ ions.

OR

In an alkaline medium, the oxygen atom is balanced by adding H2O molecule, and an equal number of ions are added on the opposite side, H+ atoms still unbalanced add OH

Step 4: Balance the charges by the addition of electrons.

Step 5: Multiply with a suitable integer such that the number of electrons gets cancelled.

Step 6: Add both the half-reactions, similar terms are subtracted, and the final equation is written.

For more details click here, Balancing Redox Reactions

Real-life Applications of Redox Reaction

Redox reactions have numerous industrial and everyday applications. A few of these applications of redox reactions are listed below.

Applications of Redox Reaction in Electrochemistry

The battery used for generating DC current uses a redox reaction to produce electrical energy.

Batteries or electrochemical cells used in our day-to-day life are also based on redox reactions. For example, storage cells are used in vehicles to supply all the electrical needs of the vehicles.

Redox Reaction in Combustion

Combustion is a type of oxidation-reduction reaction, and hence it is a redox reaction. An explosion is a fast form of combustion; hence explosion can be treated as a redox reaction. Even the space shuttle uses redox reactions. The combination of ammonium perchlorate and powdered aluminium inside the rocket boosters gives rise to an oxidation-reduction reaction.

Applications in Photosynthesis

Green plants convert water and carbon dioxide into carbohydrates, defined as photosynthesis. The reaction is given as 6CO2 + 6H2O → C6H12O6 + 6O2

In the above reaction, we can see that carbon dioxide is reduced to carbohydrates while the water gets oxidized to oxygen hence it is a redox reaction. The energy is provided by the sunlight for this reaction. This reaction is a source of food for animals and plants.

Uses of Redox Reaction

Redox Reaction are of great use in our daily life, some examples of redox reaction include:

  • Production of some important chemicals is also based on electrolysis which in turn is based on redox reactions. Many chemicals like caustic soda, chlorine, etc., are produced using redox reactions.
  • Oxidation-Reduction reactions also find their application in sanitizing water and bleaching materials.
  • The surfaces of many metals can be protected from corrosion by connecting them to sacrificial anodes, which undergo corrosion instead. A common example of this technique is the galvanization of steel.
  • The industrial production of cleaning products involves the oxidation process.
  • Nitric acid, a component of many fertilizers, is produced from the oxidation reaction of ammonia.
  • Electroplating is a process that uses redox reactions to apply a thin coating of a material on an object.
  • Electroplating is used in the production of gold-plated jewellery.
  • Many metals are separated from their ores with the help of redox reactions. One such example is the smelting of metal sulfides in the presence of reducing agents.

Related Resources,

Redox Reactions JEE Mains Questions

Q1. The number of electrons involved in the reduction of permagnate to manganese dioxide in acidic medium is

Q2. 5 g of NaOH was dissolved in deionized water to prepare a 450 ml of stock solution. What volume (in ml) of this solution would be required to prepare 500 ml of 0.1 M solution?

Q3. The density of a monobasic strong acid (Molar mass 24.2 g/mol) is 1.21 kg/L. The volume of its solution required for the complete neutralization of 25 ml of 0.24 M NaOH is,—- 10-2 ml (Nearest Integer)

Q4. The volume of 0.2 M aqueous HBr required to neutralize 10.0 ml of 0.001 m aqueous Ba(OH)2 is,

Q5. 2IO3 + xI + 12H+ –> 6I2 + 6H2. What is the value of x?

Redox Reaction- FAQs

1. What is a Redox Reaction?

The reactions that involve both oxidation and reduction reactions are called redox reactions. 

2. What are Oxidation-Reduction Reactions?

Oxidation-reduction reactions are the chemical reactions that involve transfer of electrons between the reacting species. This led to change in the oxidation state of reactant.

3. What is Redox Reaction Example?

Examples of Redox reactions include,

  • Reaction Between Hydrogen and Fluorine
  • Reaction Between Zinc and Copper Sulphate, and others

4. How to balance Redox Reaction?

Redox reactions are balanced using any of the two methods which include:

  • Oxidation Number method.
  • Ion-Exchange method.

5. What are Oxidizing Agents?

The substance that are readily reduced in a redox reaction are called oxidizing agents. They are electron-accepting species. Oxidation numbers of oxidizing agent decrease in redox reactions. Examples of the oxidizing agent include nitric acid (HNO3) and hydrogen peroxide (H2O2).

6. What are Reducing Agents?

The substance that are readily oxidized in a redox reaction are called reducing agents. They are electron-donating species. Oxidation numbers of reducing agent increases in redox reactions. Examples of reducing agents include lithium(Li) and zinc (Zn).

7. Is every chemical reaction a Redox Reaction?

No, not every chemical reaction is a redox reaction. Non-redox reactions include reactions like double decompositions, acid-base neutralization, and others.

8. What is Redox Reaction of Photosynthesis?

In Photosynthesis, the carbon dioxide molecules obtained from nature is reduced to glucose molecules and the water molecule is oxidised into free oxygen molecule. The redox reaction of Photosynthesis is given as 6CO2 + 6H2O → C6H12O6 + 6O2

9. What we have to study in Redox Reaction Class 10?

In Redox Reaction class 10 we read basic definition of oxidation, reduction, oxidizing agent, reducing agent and application of redox reaction in daily life.

10. What we have to study in Redox Reaction Class 11?

In Redox Reaction Class 11, we study advanced definition of oxidation and reduction, learn to identify the atoms going under oxidation and reduction by calculating charge, learn to balance redox reactions by half cell method and ion electron method.


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Last Updated : 18 Oct, 2023
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