Types of Chemical Reactions in Chemistry with Examples

There are different types of chemical reactions – hydrolysis, oxidation, synthesis, reduction, combustion, electrolysis, neutralization, etc.  However, we can classify all types of reactions into the following categories:

1. Combination or synthesis reaction
2. Decomposition reaction
3. Displacement reaction, and
4. Double displacement or double decomposition reaction

Types of chemical reactions in chemistry. Video by Selftution

Apart from the above, we can also classify all types of reactions based on the evolution or absorption of energy. These are endothermic or exothermic reactions. The types of reactions in which energy is evolved are called exothermic reactions. Whereas, endothermic reactions are those, where the absorption of energy takes place.

Before we study various types of reactions, it is important to know what a chemical reaction is.

WHAT IS A CHEMICAL REACTION?

A chemical reaction is a process in which two or more substances when brought in close contact with each other interact chemically to produce one or more new substances.

Definition of a chemical reaction –

A chemical reaction is a process in which two or more substances called reactants, react with each other to form one or more new substances called products. This may involve the evolution or absorption of energy.

Reactant (A) + Reactant (B) → Product (C) + Product (D)

COMBINATION OR SYNTHESIS REACTIONS

A chemical reaction in which two or more substances combine to form a single new substance is called a combination or synthesis reaction. For example,

A + B → AB

In the above reaction, a combination of substances A & B (reactants) takes place to give a molecule of a new substance AB (product). It’s important to note that most of the synthesis reactions are exothermic in nature.

There are three types of combination or synthesis chemical reactions:

1. Two elements combine to form a compound.
2. An element and a compound combine to give a new compound.
3. Two or more compounds combine to form a new compound.

Examples of all three types of combination or synthesis chemical reactions:

DECOMPOSITION REACTIONS

A decomposition reaction is one in which a compound splits into simpler substances (elements or compounds) such that the products formed do not recombine to form the original compound. For example,

AB → C + D

Here the decomposition of the molecule AB takes place to give two or more new substances C & D. It may occur in the presence of heat or light or by the passage of an electric current. Therefore, decomposition reactions are of three types –

• Thermal decomposition,
• Photo decomposition or photolysis, and
• Electrolysis

Thermal decomposition reactions are those which involve heat. Photo decomposition or photolysis is the one that involves light. Electrolysis is due to the passing of an electric current.

Heat, light, and electricity are different forms of energy that cause the breaking of bonds in the molecules of reactants to yield simpler products. Therefore, decomposition reactions are endothermic in nature.

Similar to combination reactions, based on the types of products formed, decomposition chemical reactions are also of three types:

1. A compound breaks up to form two or more elements.
2. Formation of both elements and compounds due to the breakup of a compound.
3. A compound breaks up to form two or more compounds.

Examples of all types of decomposition chemical reactions:

DISPLACEMENT REACTIONS

In a displacement reaction, a more active element displaces a less active element from a compound. In such reactions, the active element replaces one element of the reactant molecule. For example,

AB + C → CB + A

Here, C displaces A from AB, since C is chemically more active as compared to A. A displacement reaction can be exothermic or endothermic in nature. We used the reactivity series of metals and nonmetals to identify the chemical activity of an element. In the reactivity series, more active metals are at the top and least active at the bottom.

There are three types of displacement reactions:

1. A more reactive metal displaces a less active metal from its salt solution.
2. A metal more reactive than hydrogen displaces hydrogen gas from an acid.
3. A more reactive non-metal displaces a less active non-metal from its salt solution.

Examples of types of displacement chemical reactions:

DOUBLE DISPLACEMENT OR DOUBLE DECOMPOSITION REACTIONS

This is a type of chemical reaction in which two compounds in a solution state exchange their ions or radicals to form new compounds. For example,

AB + CD → CB + AD

Here, AB & CD are the two reactants molecules. They exchange their ions or radicals to form two new molecules, CB and AD. Double displacement or double decomposition reactions are of two types – precipitation reactions and, neutralization reactions.

1. Precipitation reaction: A chemical reaction in which two compounds in their aqueous state react to form an insoluble solid (a precipitate) as one of the products is called a precipitation reaction.
2. Neutralization reaction: A chemical reaction in which acid reacts with a base or an alkali to form a salt and water only is called a neutralization reaction.

Examples of types of double displacement or double decomposition chemical reactions with respect to precipitation and neutralization reactions:

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