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Redox Reactions – Definition, Types, Uses, Applications

  • Difficulty Level : Expert
  • Last Updated : 13 Dec, 2021

The oxidation states of the reactants change in redox reactions, which are oxidation-reduction chemical reactions. The term redox refers to the reduction-oxidation process. All redox reactions can be divided into two types of processes: reduction and oxidation. The redox reaction, also known as the Oxidation-Reduction reaction, always involves simultaneous oxidation and reduction events. In a chemical reaction, the material being reduced is known as the oxidizing agent, whereas the substance being oxidized is known as the reducing agent.

Oxidation is defined as the loss of electrons and the resulting increase in the oxidation state of a given reactant. Reduction is the process by which electrons are gained and the oxidation state of a reactant decreases. Oxidizing agents are electron-accepting entities that tend to suffer a reduction in redox processes. A reducing agent is an electron-donating species that tends to give electrons away. These substances are prone to oxidation. Any redox reaction may be broken down into two parts: the oxidation half-reaction and the reduction half-reaction.

General Rules Regarding Oxidation States

  1. A free element’s (uncombined element’s) oxidation state is zero.
  2. The oxidation state of a simple (monoatomic) ion is equal to the ion’s net charge. For example, the oxidation state of Cl is -1.
  3. When hydrogen is present in most compounds, it has an oxidation state of +1 while oxygen has an oxidation state of 2. The exceptions are hydrogen, which has an oxidation state of 1 inactive metal hydride (such as LiH), and an oxidation state of 1 in peroxides or -1/2 in superoxides.
  4. The algebraic total of all oxidation states in a neutral molecule must be zero. The algebraic total of the oxidation states of the individual atoms in ions must equal the ion’s charge.

Types of Redox Reactions

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. Various are some examples of these types of reactions:

2NaH → 2Na + H2

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.

Double Decomposition Reaction: The transformation of one component of a substance into two new compounds. A double replacement reaction occurs when a positive ion exchanges with another positive ion of the molecule. A combination reaction is the inverse of a decomposition reaction. The creation of a single product from two or more reactants is involved in such reactions. Endothermic and exothermic breakdown reactions are both possible. The latter, however, is more common than the former. The extraction of metals from their ores is a prominent application of decomposition processes. Zinc, for example, can be extracted from calamine via a decomposition reaction. Similarly, sodium can be obtained from sodium chloride (NaCl).

Uses of Decomposition Reaction

  • It is used to extract metals.
  • It contributes to the creation of cement.
  • It aids in the alleviation of dyspepsia.
  • It is employed in the decomposition of silver chloride in silver.
  • It is also employed in thermite welding.

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. As an example:

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. Another example is shown below.

P4 + 3NaOH + 3H2O → 3NaH2PO2 + PH3

Sample Questions

Question 1: What is called displacement reaction?

Answer:

A displacement reaction is one in which a portion of one reactor is replaced by another. A displacement reaction is also known as a substitution or metathesis reaction.

Question 2: What is a Neutralisation reaction?

Answer: 

A neutralisation reaction occurs when an acid and a base react chemically to produce a salt and water. The salt’s pH is determined by the pH of the interacting acids and bases.

Question 3: Are acid-base reactions double replacement?

Answer:

In double substitution reactions, two ionic compounds exchange anions or cations. Neutralisation reactions occur when the reactants are acid and base, and neutralisation reactions are generally favorable as long as the reaction requires a solid acid and/or base.

Question 4: What is decomposition reaction?

Answer:

Decomposition reaction is a reaction that involves the breakdown of a molecule into other components.

Question 5: What is a redox reaction?

Answer:

Redox reactions are oxidation-reduction chemical reactions in which the oxidation states of the reactants change.

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