Chemical Reaction - Definition, Types & Examples

Chemical reaction is the change in physical or chemical properties of substance to form new substance. In general a chemical reaction is due to breaking or formation of chemical bond between the atoms.

Key words: Chemical reaction, Reactant, Reagent, Product, Mechanism, Thermodynamics, Kinetics, Synthesis, Decomposition, Redox reaction, Single replacement, Double replacement,  Acid-base reactions, Combustion, Precipitation.

In this article we will learn about chemical reactions and different types of chemical reactions. Every reaction has three components: reactant,  reagent and product. 

Introduction

The substance which is consumed in the chemical reaction is known as reactant. The substance that makes the change in properties of a reactant is known as reagent. A chemical reaction yields new substance which is known as product.

Figure 1: Typical representation of chemical reaction

Any chemical reaction is studied on the basis of three aspects these are mechanism, thermodynamics and kinetics of the reaction.

Mechanism: It is a step by step description of the reaction which tells that which bond is breaking and which bond is forming. Mechanism of reaction gives idea about order of the events taking place during the course of the reaction.

Thermodynamics: It is study of energy changes occurred during the reaction. It gives idea about stability of reactants, products and intermediate compounds in the chemical reaction. It also tells that any reaction is feasible or not.

The chemical reactions follow laws of thermodynamics. If energy released during the reaction that reaction is known as exothermic reaction. The other type of reaction where energy is consumed it is known as endothermic reaction.

Kinetics: It is a study of rate of the reaction. Kinetics tells that which reaction is fast and which is slow. It helps to predict how reaction conditions can be changed to improve rate of the reaction.

Basic types of Chemical reactions

Chemical reactions can be categorized in to various types based on their mode of action these are synthesis reactions, decomposition reactions, single replacement reactions, double replacement reactions etc.

1. Synthesis

In synthesis reaction two or more reactants combine to form new product. It is written as substance A and B react with each other to form new product AB.

The example of synthesis reaction is that when hydrogen gas combine with oxygen gas to produce water.

2.    Decomposition

In this type of reaction a complex compound break down into two or more simple compounds. It is a reverse reaction of synthesis reaction. It can be written as a complex substance AB undergo decomposition reaction to form its simple parts A and B. 

For example, hydrogen peroxide slowly decomposes at room temperature to produce water and oxygen gas.

3.    Single replacement

In this type of reactions one element of the compound is replaced by another compound to produce new compound. It can be written as when a compound AB reacts with compound C it gives formation of new compounds AC and B. 

For example, a reaction of magnesium and hydrochloric acid produces magnesium chloride as hydrogen gas.

4.    Double replacement

In this type of reaction two compounds reacts in such a way that anions and cations of these compounds switch their places to form new compounds. It can be written as when a compound AB reacts with compound CD to form new compounds AC and BD. 

For example, barium chloride (BaCl₂) reacts with magnesium sulphate (MgSO₄) to form barium sulphate (BaSO₄) and magnesium chloride (MgCl₂). Here anion (SO4²⁻) switch places with another anion (2Cl⁻) form BaSO₄ and MgCl₂.  

5.    Combustion  

In this type of reaction a substance reacts with oxygen gas to produce oxides and release energy in the form of heat or light. For example in an alcohol lamp ethanol reacts with oxygen present in the air to produce carbon dioxide and water vapour. Also reaction release energy in the form of heat and light. 

6.    Redox reaction

It is a combination of two reactions that is oxidation and reduction. When there is an increase in oxidation state of species takes place it is called as oxidation. If there is decrease in the oxidation state of species takes place it is called as reduction. For example, sodium metal reacts with chlorine gas to form sodium chloride.

 

Here sodium looses one electron so its oxidation state increases from 0 to +1. On the other hand Chlorine atom gains one electron so its oxidation state decreases from 0 to -1. Therefore we can say that in this redox reaction, sodium metal undergoes oxidation and chlorine gas undergoes reduction reaction.

7.    Acid-base reactions

It is also known as neutralization reaction. In this reaction acid reacts with base to form neutral compound. For example hydrochloric acid reacts with sodium hydroxide to produce sodium chloride and water. 

8.    Precipitation

In this type of reactions the product formed has very less solubility in the reaction solvent. Therefore at initial stage when there is no product formation the reaction mixture is clear solution. After some time when the product start forming that time reaction will be turbid. At the end of reaction when complete formation of product takes place, it will not be soluble in reaction solvent. So the product solidifies and settles at the bottom of the flask. In this reaction pure product is obtained by filtration.

Figure 2: Precipitation reaction

For example, aqueous solution of silver nitrate reacts with aqueous solution of potassium chloride to produce silver chloride as white precipitate and potassium nitrate. The solution can be filtered to get pure silver chloride.

 

To summarize this topic

A chemical reaction is the change in physical or chemical properties of substance to form new substance.

Any chemical reaction is studied on the basis of three aspects these are mechanism, thermodynamics and kinetics of the reaction.

Based on their mode of action chemical reactions are categorized in to different types.

That's all for this topic. If you have any questions please feel free to ask me. Also suggest me if any changes or additions are required. Thank you..!