Introduction to Oxidation and Reduction Reactions
An oxidation reduction reaction is a type of chemical reaction that constitutes a transfer of electrons within two elements. It is a type of chemical reaction that involves the change in the oxidation number of an ion, atom, or molecule by the loss or gain of an electron. Redox reactions form the core of the sustenance of life on earth, supporting some of the most crucial chemical reactions such as photosynthesis, respiration, corrosion, and combustion. Oxidation and reduction (redox) reactions are important because they ignite the natural or biological plus artificial energy sources on this planet. The oxidation of molecules releases typically large amounts of energy by removing hydrogen and replacing it with oxygen.
Oxidation Reaction
Oxidation is the lack of electrons during a reaction by an atom, molecule, or ion. Oxidation happens when the oxidation state of an atom, molecule, or ion is enhanced. The opposite method is called reduction, which results when there is a gain of electrons. According to the modern definition, the reaction in which oxygen is included is still oxidation. Therefore oxidation can be defined as the loss of a hydrogen atom, while the gain of a hydrogen atom is termed as reduction. An example of oxidation reaction can be the transformation of ethanol to ethanal: CH₃CH₂OH → CH₃CHO
Ethanol is regarded as oxidised because it loses hydrogen. By converting the equation, ethanal can be lessened by adding hydrogen to it to form ethanol.
Reduction
Reduction is a chemical reaction that includes the electrons gained by one of the atoms required in the reaction between two chemicals. It refers to the electron-accepting element since the electron-accepting element’s oxidation state is lowered by gaining an electron. An example of a reduction is when iron reacts with oxygen, forming iron oxides, also known as rust. This is called a redox reaction. By employing carbon monoxide, a blast furnace can reverse the reaction, as it can serve as the reducing agent for the iron.
Redox Reaction Definition
Redox definition is a kind of chemical reaction in which the atom’s oxidation states are altered. Redox reactions are depicted by the formal exchange of electrons among different species of chemicals, where one species experiences electron loss (oxidation) (reducing agent) and the other electron species experiences electron gain (reduction) (oxidising agent). The term “redox” comes from two ideas associated with electron transfer: reduction and oxidation. There are also five types of redox reactions: combination, decomposition, displacement, combustion, and disproportion.
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Redox reactions can happen comparatively slowly, as in the formation of rust, or much more quickly, as in the case of burning fuel. There are simple redox methods, such as the oxidation of carbon to produce carbon dioxide (CO₂) or the conversion of carbon by hydrogen to produce methane (CH₄), and more complicated processes such as the oxidation of glucose (C₆H₁₂O₆) in the human body. The investigation of bond energies and ionisation energies in water allows the calculation of the redox potentials.
Aldehyde
Aldehydes are a group of organic compounds in which a carbon atom combines a single bond with a hydrogen atom, a double bond with an oxygen atom, and a single bond with a different atom or group of atoms. The double bond within carbon and oxygen is characteristic of all aldehydes, known as the carbonyl group. Many aldehydes have pleasing odours, and in law, they are procured from alcohols by dehydrogenation, from which process came the name aldehyde.
Aldehydes can be subdued to primary alcohols (RCHO → RCH2OH) with many reducing agents; the most commonly used are lithium aluminium hydride (LiAlH4), hydrogen (H2) or sodium borohydride (NaBH4) with the help of transition catalysts such as Ni (nickel), Pd(palladium), Pt (platinum), or Rh (rhodium).
Oxidation of Aldehydes
There is a wide variety of reagents that can induce the oxidation of aldehydes to carboxylic acids. The most common reagent for this change is CrO3 in aqueous acid, also termed as Jones Reagent. Oxidation reactions of aldehydes are less relevant than reductions. Alcohols may be oxidised to yield aldehydes, ketones, and carboxylic acids. The oxidation of organic compounds usually extends the number of bonds from carbon to oxygen, and it may reduce the number of bonds to hydrogen.
FAQs on Oxidation and Reduction Reactions
1. What are oxidation and reduction reactions in chemistry?
In chemistry, oxidation is a process that involves the loss of electrons by a chemical species (atom, ion, or molecule), resulting in an increase in its oxidation state. Conversely, reduction is a process that involves the gain of electrons, leading to a decrease in the oxidation state. These two reactions always occur together in a single reaction, known as a redox reaction.
2. How can you identify if a substance is oxidised or reduced in a chemical reaction?
You can identify oxidation and reduction by observing the change in the oxidation number of an element during the reaction.
- If the oxidation number of an element increases, the substance has been oxidised.
- If the oxidation number of an element decreases, the substance has been reduced.
For example, in the reaction Zn + Cu²⁺ → Zn²⁺ + Cu, Zinc's oxidation number increases from 0 to +2 (oxidation), while Copper's decreases from +2 to 0 (reduction).
3. What is the difference between an oxidising agent and a reducing agent?
The main difference lies in their function within a redox reaction:
- An oxidising agent (or oxidant) is a substance that causes oxidation by accepting electrons from another substance. In the process, the oxidising agent itself gets reduced.
- A reducing agent (or reductant) is a substance that causes reduction by donating electrons to another substance. In the process, the reducing agent itself gets oxidised.
4. Why are oxidation and reduction reactions always considered to occur simultaneously?
Oxidation and reduction are two halves of a single process involving the transfer of electrons. A substance cannot lose electrons (oxidation) unless another substance is present to accept those electrons (reduction). Electrons are not created or destroyed in a chemical reaction. Therefore, the loss of electrons by one species must be exactly balanced by the gain of electrons by another, making the two processes inseparable.
5. What are some important real-world examples of oxidation-reduction reactions?
Redox reactions are fundamental to many natural and industrial processes. Some key examples include:
- Corrosion: The rusting of iron is an oxidation process where iron reacts with oxygen and water.
- Photosynthesis: Plants convert carbon dioxide and water into glucose and oxygen, where CO₂ is reduced and H₂O is oxidised.
- Respiration: Living organisms oxidise glucose to produce energy, carbon dioxide, and water.
- Combustion: The burning of fuels like wood, petrol, or natural gas is a rapid oxidation process.
- Batteries: Electrochemical cells in batteries generate electricity through controlled redox reactions.
6. How is the concept of oxidation number more comprehensive than classical definitions?
The classical definitions describe oxidation as the addition of oxygen or removal of hydrogen, and reduction as the reverse. While useful, this is limited to reactions involving these specific elements. The oxidation number concept is more comprehensive because it defines redox reactions based on the transfer of electrons, which is the underlying principle. This allows us to identify and analyse redox reactions even when oxygen or hydrogen are not involved, making it a universally applicable model.
7. Are all combustion reactions also redox reactions? Explain why.
Yes, all combustion reactions are a specific type of redox reaction. Combustion is defined as a rapid reaction between a substance and an oxidant, usually oxygen, to produce heat and light. In this process, the substance being burned (the fuel) is oxidised, and the oxygen is reduced. For example, in the burning of methane (CH₄), carbon is oxidised from an oxidation state of -4 to +4 (in CO₂), and oxygen is reduced from 0 to -2 (in H₂O).
8. What are the main types of redox reactions as per the NCERT syllabus?
According to the CBSE/NCERT curriculum for the 2025-26 session, redox reactions are broadly classified into four main types:
- Combination Reactions: Where two or more substances combine to form a single compound, like C + O₂ → CO₂.
- Decomposition Reactions: Where a compound breaks down into two or more simpler substances, like 2H₂O → 2H₂ + O₂.
- Displacement Reactions: Where an ion or atom in a compound is replaced by an ion or atom of another element, like Zn + CuSO₄ → ZnSO₄ + Cu.
- Disproportionation Reactions: Where an element in one oxidation state is simultaneously oxidised and reduced, like 2H₂O₂ → 2H₂O + O₂.
