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Writing a Chemical Equation

Aug 24, 2022

Key Concepts

  • Chemical equation
  • Skeleton equation
  • Stoichiometric coefficients
  • Endo and exothermic reactions
  • Reversible & Irreversible reactions
  • Homogenous and heterogenous reactions


Chemical Equation: 

A chemical equation is a representation of a chemical reaction to show the change that occurred in a compound, separated by an arrow.. The initial chemicals before the reaction are called the reactants and the final products of the chemicals formed after the reaction are called the products. The equation uses chemical symbols to denote the reaction. 

An example for the chemical reaction is  

N2  +  3H2 ———>2NH3 

Here, the N and H are called the reactants and NH3 is called the Product. 

Word Equation: 

When the initial reacting substances and the final substances of a chemical reaction are represented with their names, it is known as a word equation. In the word equation, the complete word is written in the equation.  


The example for the word equation is  

Magnesium  +  Oxygen ———–>  Magnesium oxide 

Formula Equation: 

It is the symbolic representation of the reacting substances and the obtained substances by using symbols or formulae. The balancing of the number of atoms in the equation is not verified as mandatory.  

The example for the formula equation or the Skeletal chemical equation is  

Mg  +  O  ————->  MgO 


Importance of the chemical equation: 

Chemical equations are made more concise and useful by using symbols and formulae of the substances. 

Characteristics of the Chemical equation: 

Chemical equations are the representation of a chemical change. The chemical equation has to contain the correct formula of the substances. The chemical equation gives information about reactants and products. 

Representation of the chemical equation: 

Magnesium burning in the presence of Oxygen gives Magnesium Oxide.  

Its word equation can be represented by symbol equation as follows :  

Mg  +  O  ————->  MgO 


The substances or chemicals that are on the left side of the equation are called reactants. They undergo change during the reaction. 


The substances that are written on the right side of the chemical equation are called the products. They are formed due to the reaction. 

Reactants and the products can be in any state. They can be in solid, liquid, gas or even aqueous state. 

Arrow Indication: 

Arrow in a chemical equation is shown or pointed from reactants towards the products which show the direction of change. 

Fig 1

The number before the chemical symbol is the coefficient and the number after the chemical symbol in subscript form is the number of atoms present in the element. The chemical substances on the left of the arrow are the reactants and the chemical substances on the right of the arrow are called the products. The state of the chemical is written in brackets in short form. 

Types of chemical reactions: 

Based on the physical state of reactants and products in a chemical reaction, reactions can be of two types :  

  • Homogeneous reaction 
  • Heterogeneous reaction. 

Homogeneous reaction: 

If all the reactants and products in a chemical reaction exist in the same physical state, then such an equation is called a Homogeneous equation. 

Heterogeneous reaction: 

If all the reactants and products in a chemical reaction exist in different physical states, then such an equation is called a Heterogeneous equation. 

Reversible and irreversible reactions: 

Reversible reactions are those in which the product obtained can be reversed to reactants, again. Irreversible reactions are presented with a single arrow-like general reaction. Reversible reactions are represented with a double-headed arrow.  

Every chemical reaction during their process either take the heat energy to process the reaction or releases the heat energy to process the reaction. 

Exothermic Reaction: 

Exothermic reactions are those in which the reactants have high energy and lose energy to form the products. In such chemical reactions  heat energy is released during formation of the products.  

Endothermic reaction: 

Endothermic reactions are those in which reactants have low energy and gain energy to form products. The chemical in which the substances form the products requires heat energy to process the reaction.  

Driving force for the chemical reaction: 

A chemical reaction takes place due to the difference in energy between reactants and products. 

Which properties of the chemicals affect the chemical reaction? 

Some of the chemical reactions require the support of other chemicals in a reaction process but those chemicals do not react in the reaction. Such chemicals are called the catalyst. With the catalyst, there are some other properties that affect the reaction like enthalpy and heat energy.  


  • Chemical equation is the symbolic representation of reactants and products in a chemical reaction.
  • In a chemical reaction, substances present on left hand side are reactants and substances present on right hand side are products.
  • Reactions can be homogenous or heterogenous based on the physical state of reactants and products.
  • Reactions can be exothermic or endothermic based on the release or absorption of heat energy.


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