How Do Redox Reactions Work in Chemistry?
What is Redox Reaction
Many chemical reactions involve transfer of electrons from one chemical substance to another. These electron transfer reactions are termed as oxidation-reduction or Redox reaction, or those reactions which involve oxidation and reduction both simultaneously are known as oxidation and reduction/ Redox reaction. Redox reaction can also be termed as an increase in oxidation number or decrease in oxidation number simultaneously.
Oxidation and Reduction
There are mainly four four concepts of oxidation and reduction reaction:
A. Classical Concept: According to this concept, oxidation and reduction can be explained as:
Oxidation
Oxidation is a process which involves:
Addition of oxygen
Removal of hydrogen
Addition of electronegative elements
Removal of electropositive elements
Increment in oxidation state of electropositive element.
Reduction
Reduction is a process which involves:
Removal of oxygen
Addition of hydrogen
Removal of electronegative elements
Addition of electropositive elements
Decrement in oxidation state of electropositive elements
B. Modern Concept or Electronic Concept
Oxidation
According to this concept the process which involves the loss of one or more electrons from an atom or an ion or molecules is called oxidation.
Reduction
According to this concept, the process which involves gain of one or more electrons by an atom or ion molecule is called reduction.
C. Valency Concept of Oxidation and Reduction
Oxidation
According to this concept, it is the process in which increase in positive valency or decrease in negative valency of a substance takes place called oxidation.
Reduction
According to this concept,it is the process in which decrease in positive or increase in negative charge of a substance takes place called reduction.
D. Oxidation Number Concept
Oxidation
According to this concept, the oxidation number of elements increases.
Reduction
According to this concept oxidation number of elements decreases.
Oxidising Agent or Oxidants
The Substance which accept electrons in a chemical reaction i.e electron acceptors are oxidising agents:
Oxidising agents are lewis acid.
Substance which can oxidise others and reduce themselves.
Substance which shows decrement in oxidation number.
All high electronegative elements like N, O, F, Cl, etc are oxidants.
All metallic oxides are oxidants.
Some non metallic oxides are also oxidants like CO2, CaO, etc.
Reducing Agents or Reductant
The substances which donate electrons in a chemical reaction are reducing agents i.e electron donors are reducing agents.
Reducing agents are Lewis base.
Substances which can reduce others and oxidise themselves.
Substance which shows decrement in oxidation number.
All metal like K, Mg, Ca, etc are examples of reductants.
All metallic hydrides are examples of reductants.
All hydro acids are reductants. Example: HF, HCl, HBr, etc.
Oxidation Number
It represents the number of electrons gained or lost by an atom when it changes in compound from free state. It is also defined as charge on an atom when the atom is in combining state.
If electrons are gained by an atom in the formation of compounds the oxidation number is given a negative sign.
If electrons are loose by atom in the formation of compounds the oxidation number is given a positive sign.
It represents real charge in case of ionic compounds and imaginary charge in case of covalent compounds.
Maximum oxidation number is equal to the group number in the periodic table.
Minimum number of oxidation states is equal to group number i.e (-8).
Oxidation State
Oxidation state of an atom is defined as the oxidation number per atom for all practical purposes. Oxidation state is often expressed as the oxidation number.
Types of Redox Reactions
Intermolecular Redox Reaction
When oxidation and reduction take place separately in the different compounds called intermolecular redox reactions.
SnCl2+ 2FeCl3-------SnCl4+2FeCl2
Intramolecular Redox Reaction
During chemical reaction if oxidation and reduction take place in a single compound then reaction is called intramolecular redox reaction.
2KClO3------KCl+3O2
Disproportionation Reaction
When reduction and oxidation take place on the same elements of the compound is called disproportionation reaction.
H2O2--------H2O+3O2
Multiple Choice Questions
1. Oxidation number of nitrogen in NH2OH:
0
+1
-1
-2
Answer: (C)
2. Which one has same oxidation state in all of its compound:
Hydrogen
Fluorine
Carbon
Oxygen
Answer: (b)
3. Oxidation number of C in HCN:
+2
-3
+3
Zero
Answer: (a)
4. If elements is in lowest oxidation state under proper condition it act as a:
Reducing agent
An Oxidising agent
Both of them
None of them
Answer: (a)
FAQs on Redox Reaction: Meaning, Types & Real-Life Examples
1. What is a redox reaction in simple terms, as per the CBSE syllabus?
A redox reaction is a type of chemical reaction where both oxidation (loss of electrons or an increase in oxidation state) and reduction (gain of electrons or a decrease in oxidation state) occur simultaneously. Essentially, it involves the transfer of electrons between two chemical species. A classic example is the reaction between zinc metal and a copper sulphate solution: Zn + CuSO₄ → ZnSO₄ + Cu. Here, zinc is oxidised, and copper is reduced.
2. What is the difference between an oxidising agent and a reducing agent?
The key difference lies in their function during a redox reaction:
An oxidising agent (or oxidant) is a substance that accepts electrons and gets reduced itself. By accepting electrons, it causes the oxidation of another substance. Its own oxidation number decreases during the reaction. Examples include O₂, Cl₂, and KMnO₄.
A reducing agent (or reductant) is a substance that donates electrons and gets oxidised itself. By donating electrons, it causes the reduction of another substance. Its own oxidation number increases. Examples include H₂, Na, and LiAlH₄.
3. What are the main types of redox reactions explained in NCERT Chemistry?
The primary types of redox reactions students learn about are:
Combination Reaction: Two or more substances combine to form a single compound. For example, C(s) + O₂(g) → CO₂(g), where carbon is oxidised and oxygen is reduced.
Decomposition Reaction: A compound breaks down into two or more simpler substances. For example, 2H₂O(l) → 2H₂(g) + O₂(g).
Displacement Reaction: An ion or atom in a compound is replaced by an ion or atom of another element. For example, Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s).
Disproportionation Reaction: A reaction where an element in a single oxidation state is simultaneously oxidised and reduced. For example, in the reaction 2H₂O₂(aq) → 2H₂O(l) + O₂(g), oxygen in peroxide (oxidation state -1) is reduced to -2 (in H₂O) and oxidised to 0 (in O₂).
4. What are some common examples of redox reactions in everyday life?
Redox reactions are fundamental to many daily processes:
Respiration: The metabolic process where glucose is oxidised in our cells to produce energy (ATP), carbon dioxide, and water.
Photosynthesis: The reverse of respiration, where plants reduce carbon dioxide and oxidise water using sunlight to create glucose and oxygen.
Rusting of Iron: Iron objects slowly oxidise in the presence of air and moisture to form iron oxide, or rust.
Combustion: Burning of fuels like wood, petrol, or LPG is a rapid redox reaction where the fuel is oxidised by oxygen.
Batteries: The generation of electricity in batteries and cells relies on redox reactions occurring at the electrodes.
5. Why must oxidation and reduction always occur together in a chemical reaction?
Oxidation and reduction must occur simultaneously because they describe the two inseparable parts of an electron transfer. For one substance to lose electrons (oxidation), another substance must be present to gain those same electrons (reduction). Electrons cannot be simply created or destroyed in a chemical reaction; they are only transferred. Therefore, one process cannot happen in isolation, making them two halves of a complete redox reaction.
6. How can you identify if a chemical reaction is a redox reaction by using oxidation numbers?
To identify a redox reaction, you can follow these steps:
Assign the oxidation number to every atom in both the reactants and the products according to standard rules.
Compare the oxidation number of each element on the reactant side with its oxidation number on the product side.
If the oxidation number of any element changes during the reaction, it is a redox reaction. An increase in oxidation number indicates oxidation, while a decrease indicates reduction.
If no element's oxidation number changes, the reaction is a non-redox reaction.
7. What is the importance of redox reactions in biological systems like the human body?
Redox reactions are vital for life itself. Their primary importance in biological systems is in energy metabolism. The central process of cellular respiration involves a series of complex redox reactions where glucose and other food molecules are oxidised. This controlled oxidation releases the energy stored in their chemical bonds, which is then captured in the form of ATP (adenosine triphosphate), the energy currency that powers all cellular activities, from muscle contraction to nerve impulses.
8. Is every combustion reaction also a redox reaction? Explain with an example.
Yes, all combustion reactions are a type of redox reaction. In combustion, a substance (the fuel) reacts with an oxidant (usually oxygen) to produce heat and light. During this process, the fuel is oxidised, and the oxygen is reduced. For example, in the burning of methane (CH₄):
CH₄ + 2O₂ → CO₂ + 2H₂O
Here, the oxidation state of Carbon increases from -4 in CH₄ to +4 in CO₂, and the oxidation state of Oxygen decreases from 0 in O₂ to -2 in CO₂ and H₂O. Since oxidation states change, it is a redox reaction.
