Chemical Reactions: Definition, Types, Equations and Examples

The curdling of milk, rust formation on iron, process of food cooking, even the act of breathing are all examples of Chemical Reactions. We may not realise it but chemical reactions are constantly occuring all around us, even within our own body. Understanding these reactions gives us a better idea of how the world around us functions. 

From rusting to decomposition, chemical reactions help us gain detailed information about molecular interactions and how they cause a substance to change its form. In this article we will learn about chemical reactions and their types and examples in more detail.

Keyterms: Milk, Rust formation, Iron, molecular interaction, making or breaking of bonds, Atoms, Curd

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What is a Chemical Reaction?

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When a chemical substance is transformed into another, the entire process is referred to as Chemical Reaction. These are the chemical changes where reactants transform into products by either making or breaking of bonds (or both) between different atoms. Even some of the reactions that occur on daily basis like rusting of iron, preparation of curd from milk, etc. are kinds of chemical reactions.

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Basic Concepts of Chemical Reactions

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Apart from understanding physical and chemical changes, there are some more important concepts that should be kept in mind before studying more about chemical reactions and equations. ​

1. Endothermic and Exothermic Process: A chemical reaction in which heat is absorbed from the surroundings is called an endothermic reaction. Melting of ice is a common example of an endothermic reaction. In an exothermic reaction, energy is released in the form of heat or light. Burning of a substance is an example of this type of chemical reaction.
2. Rate of Reaction: There are some important factors that determine the rate of a chemical reaction which are: temperature, pressure and concentration of reactants.
3. Law of Conservation of Mass: According to the law of conservation of mass, in any chemical reaction, the total mass or mass of the reactants participating is equal to the total mass of the products formed after the reaction.
4. Reactants and Products: Reactants and products are two important components of any chemical reactions. The chemical substance that initiates or participate in a reaction is called reactants. The new substance formed after the chemical reaction is called products.

To understand this, let us take a chemical reaction: H₂ + Cl₂ → 2HCl. Here, in this reaction, the substances on the left (H₂ and Cl₂) are the reactants while the new substance (2HCl) formed after the chemical reaction is a product.

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Properties of Chemical Reaction

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A chemical reaction can be explained by keeping in view the following observations:

a) Evolution of Gas: The chemical reaction that occurs between zinc and dilute sulphuric acid is characterized by the evolution of hydrogen gas.

b) Change in Temperature: The chemical reaction occurring between quick lime water to create slaked lime is due to a temperature change.

c) Formation of a precipitate: When barium chloride solution and sulphuric acid react, a white precipitate of barium sulphate is formed.

d) Change in color: The chemical reaction occurring between citric acid and purple-colored potassium permanganate solution undergoes color change. From purple color, it changes to being colorless.

e) Change of state: In the candle wax combustion reaction, there is a change in the state from solid to liquid and gas.

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Types of Chemical Reactions

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Keeping various factors in mind, chemical reactions are divided into several categories.:

• Combination Reaction: In these reactions, two or more reactants combine together for creating one product. 
• Decomposition Reaction: Reactions where one compound decomposes in two or more compounds or elements are referred to as Decomposition Reaction.
• Thermal Decomposition: The decomposition of a substance when they are heated are being referred to as Thermal Decomposition.
• Electrolytic Decomposition: Reactions where compounds decompose into simpler compounds due to the passing of electricity, are known as Electrolytic Decomposition. This is also known as Electrolysis.
• Photolysis or Photo Decomposition Reaction: In these reactions, a compound decomposes due to the presence of sunlight. This reaction is being known as Photolysis or Photo Decomposition Reaction.
• Single Displacement Reaction: Chemical reactions where a more reactive element displaces a less reactive element from a compound, are referred to as Displacement Reactions. They are also referred to as Substitution Reaction Replacement reactions.
• Double Displacement Reaction: Reactions, where ions are exchanged between two reactants resulting in the creation of new compounds, are known as Double Displacement Reactions.
• Precipitation Reaction: The reaction that occurs when a precipitate is formed by the combination of an aqueous solution of two salts is called Precipitation Reaction.
• Neutralization Reaction: In this kind of reaction, an acid reacts with a base to form salt and water by an exchange of ions is called Neutralization Reaction.
• Oxidation Reaction: Adding oxygen or non-metallic element or removing hydrogen or metallic element from a compound is referred to as Oxidation. 
• Redox Reaction: A reaction in which a reactant gains one or more electrons is known as a reduction reaction.
• Redox Reactions: A type of chemical reaction in which both oxidation and reduction of a species occur simultaneously is called a redox reaction.

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Chemical Reactions and Equations

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A word equation is defined as a chemical reaction expressed in words instead of chemical formulas. It helps in identifying the reactants and products in a chemical reaction.

For example,

Sodium + Chlorine → Sodium chloride

or, 

2Na(s) + Cl₂(g) → 2NaCl(s)

In the above equation, Sodium reacted with chlorine to form sodium chloride.

Symbols of elements and their valencies

• A symbol is defined as the chemical code for an element. Each element has one or two-letter atomic symbols that is the abbreviated form of their name. 
• Valency is the combining capacity of an element and can be considered as the number of electrons lost, gained, or shared by an atom on getting combined with another atom to form a molecule.

Read More:- Chemical Reactions and Equations Important Questions