How to represent a chemical reaction?

REPRESENTATION OF A CHEMICAL REACTION

In the previous post, we have learnt about chemical reactions - it's definition and concept. Now, we will focus our discussion on the different ways to represent a chemical reaction.

Table of Contents

1. Introduction
2. Different ways to write a chemical reaction
1. Word - Equation
2. Chemical Equation
3. Rules of writing a chemical equation
4. Moving ahead...

Introduction

What happens when coal (carbon) is burnt in the presence of air?

The carbon present in the coal reacts with the oxygen from the atmosphere to give carbon dioxide gas.

This description of a chemical reaction in a sentence form is quite long, tedious and consumes a significant amount of time to write.
In order to simplify the process, a shorter form of this description is required which is easy to write and contains all the vital information's of the chemical reaction. Let us have a look on different ways to do so.

Different ways to write a chemical reaction -

A chemical reaction can be represented in the following two ways :-

1. Word Equation
When we represent a chemical reaction using the chemical names of the reactants and products, it is called a word equation.
For Example -
1. When coal is burnt in the presence of air, it releases carbon dioxide gas. The word equation for this chemical reaction will be written as:



2. When silver chloride is kept in sunlight, it decomposes into silver and chlorine. The word equation for this chemical reaction will be written as:
   


2. Chemical Equation
When we represent a chemical reaction using the chemical formula of the reactants and products, it is called a chemical equation.
For Example –
1. When coal is burnt in the presence of air. The chemical equation for this reaction will be written as:
   


2. When silver chloride is kept in sunlight. The chemical equation for this reaction will be written as:
   

Generally, the chemical equation is highly preferred than the word equation to represent a chemical reaction as the latter is more concise, useful and easier to write.

Rules of writing a chemical equation –

While writing a chemical equation of a reaction, following rules are to be kept in mind :

1. The reactants are always written on the left-hand side (LHS).
2. The products are always written on the right-hand side (RHS).
3. An arrowhead (→) pointing from reactants to products shows the direction of the reaction.
4. In case of more than one reactant or product, a plus (+) sign is used between them.
5. The number of atoms / ions of each and every element must be equal (balanced) on both sides of the equation.
6. Specific reaction conditions, like temperature, pressure, catalyst etc. for the reaction are indicated above / below the arrowhead.
7. The physical states of reactants and products can be mentioned with their chemical formula. The solid, liquid, gaseous and aqueous states are represented by the notations (s), (l), (g) and (aq) respectively.
   • The word aqueous (aq) is written if the reactant or product is present as a solution in water.
   • If a gas is evolved during a chemical reaction, it can also be represented by an upward arrow (↑).
   • If a precipitate is formed during a chemical reaction, it is represented by a downward arrow (↓).

Moving ahead...

What happens when a magnesium ribbon is burnt in air?

The magnesium ribbon burns with a dazzling white flame and changes into a white powder called magnesium oxide. It is due to the reaction of magnesium with the oxygen present in the air.
The chemical reaction can be represented as :

Here, you may see that two types of chemical equations are given - skeletal and balanced chemical equation.
Also, in the balanced chemical equation coefficient "2" is prefixed before the chemical formula of 'Mg' in the reactants and 'MgO' in the product.

1. Why have we done so?
2. What does the coefficient mean in a balanced chemical equation?

To get the answer of these questions refer to the balancing of a chemical equation.

 Related Articles 

• Balancing a Chemical Equation
• Chemical Reactions - Definition and Concept
• Chemical Formula of Common Chemical Compounds.

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