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

Chemical Reactions

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  • 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

Chemical Reaction

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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

Many Physical Chemists

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  • 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

Reductant Transfers Electrons

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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