Basic Chemistry: Chemical Reactions, Reaction Mechanism, Redox

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Learning Outcomes

After studying this lesson, you shall be able to:

  • Reactions
  • Redox reactions


  • During chemical reactions, bonds between atoms break and form resulting in different substances with different properties.
  • In a blast furnace, iron oxide, a compound, reacts with carbon monoxide to form iron, one of the chemical elements, and carbon dioxide.
Chemical Reactions
  • When a chemical substance is transformed as a result of its interaction with another substance or energy, a chemical reaction is said to have occurred.
  • Chemical reaction is therefore a concept related to the ‘reaction’ of a substance when it comes in close contact with another, whether as a mixture or a solution; exposure to some form of energy, or both.
  • It results in some energy exchange between the constituents of the reaction as well as with the system environment which may be designed vessels which are often laboratory glassware.
  • Chemical reactions can result in the formation or dissociation of molecules, that is, molecules breaking apart to form two or smaller molecules, or rearrangement of atoms within or across molecules.
  • Chemical reactions usually involve the making or breaking of chemical bonds.
  • Oxidation, reduction, dissociation, acid-base neutralization and molecular rearrangement are some of the commonly used kinds of chemical reactions.
  • A chemical reaction can be symbolically depicted through a chemical equation.
  • While in a non-nuclear chemical reaction the number and kind of atoms on both sides of the equation are equal, for a nuclear reaction this holds true only for the nuclear particles viz. protons and neutrons.
Chemical Reaction

Reaction Mechanism

  • The sequence of steps in which the reorganization of chemical bonds may be taking place in the course of a chemical reaction is called its mechanism.
  • A chemical reaction can be envisioned to take place in a number of steps, each of which may have a different speed.
  • Many reaction intermediates with variable stability can thus be envisaged during the course of a reaction.
  • Reaction mechanisms are proposed to explain the kinetics and the relative product mix of a reaction.


  • Many physical chemists specialize in exploring and proposing the mechanisms of various chemical reactions.
  • Several empirical rules, like the Woodward-Hoffmann rules often come handy while proposing a mechanism for a chemical reaction.
  • Given below is the mechanism of SN1 reaction.
Many Physical Chemists
  • According to the IUPAC gold book a chemical reaction is a process that results in the interconversion of chemical species ″ .
  • Accordingly, a chemical reaction may be an elementary reaction or a stepwise reaction.


  • It is a concept related to the ability of atoms of various substances to lose or gain electrons.
  • Substances that have the ability to oxidize other substances are said to be oxidative and are known as oxidizing agents, oxidants or oxidizers.
  • An oxidant removes electrons from another substance. Similarly, substances that have the ability to reduce other substances are said to be reductive and are known as reducing agents, reductants, or reducers.
  • A reductant transfers electron to another substance and is thus oxidized itself.
  • And because it “donates” electrons it is also called an electron donor.
  • Oxidation and reduction properly refer to a change in oxidation number-the actual transfer of electrons may never occur.
  • Thus, oxidation is better defined as an increase in oxidation number, and reduction as a decrease in oxidation number.
Reductant Transfers Electrons


1. Which among these are the kinds of chemical reactions:

  1. Dissociation
  2. Acid-base neutralization
  3. Molecular rearrangement
  4. All of the above

Answer: All of the above

2. Substances that have the ability to oxidize other substances are called:

  1. Oxidants
  2. Oxidiser
  3. Both
  4. none

Answer: Both


#Redox reactions

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