Question

What are the steps involved in balancing a chemical equation? Explain with examples.

Answer 1

Part 1: Chemical Equation

The representation of a chemical reaction using and formulae of the elements or compounds which are involved in the reaction is known as a chemical equation.

For example, The burning of magnesium can be stated as the magnesium ribbon interacting with fire and transforming into ashes. in order to shorten this, scientists came up with a word e equation like,

$\mathrm{Magnesium}+\mathrm{Oxygen}\to \mathrm{Magnesium}\mathrm{oxide}$

But the chemical equation can be written as

$\underset{\mathrm{Magnesium}}{\mathrm{Mg}\left(\mathrm{s}\right)}+\underset{\mathrm{Oxygen}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{Magnesium}\mathrm{Oxide}}{\mathrm{MgO}\left(\mathrm{s}\right)}$

Here, the number of elements on the reactant side is not equal to the number of elements on the product side. so this is an unbalanced chemical equation. it does not obey the law of conservation of mass.

In order to make the equation obey the law of conservation of mass, we have to balance the chemical equation.

Part 2: Balancing a chemical equation

Consider the reaction of burning of magnesium in the presence of oxygen,

1. Calculate the number of atoms of each element in the reactants and products

Element	Number of atoms in reactants	Number of atoms in products
$\mathrm{Mg}$(magnesium)	1	1
$\mathrm{O}$(oxygen)	2	1

In the table, we can see that two oxygen atoms are taking part in the reaction to form one molecule of magnesium oxide. we know only one oxygen atom is enough to react with one molecule of oxygen. but we have two oxygen atoms here, the remaining one cannot be destroyed. so if there are two oxygen atoms here, we need two oxygen to combine with each oxygen atom.

2. To balance the oxygen atoms on both sides of the equation, multiply the product $\mathrm{Mg}$ by 2

Element	Number of atoms in reactants	Number of atoms in products
$\mathrm{Mg}$(magnesium)	1	1 X 2 = 2
$\mathrm{O}$(oxygen)	2	1 X 2 =2

$\mathrm{Mg}\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2\mathrm{MgO}\left(\mathrm{s}\right)$ Now the number of oxygen atoms is balanced on both sides. but the number of magnesium atoms on both sides is not balanced

3. To balance the magnesium atoms on both sides of the equation, multiply $\mathrm{Mg}$ in the reactants by 2

Element	Number of atoms in reactants	Number of atoms in products
$\mathrm{Mg}$(magnesium)	1 X 2 = 2	2
$\mathrm{O}$(oxygen)	2	2

$2\mathrm{Mg}\left(\mathrm{s}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\to 2\mathrm{MgO}\left(\mathrm{s}\right)$ thus the chemical equation is now balanced

The physical states of the reactants and products are mentioned to make it more informative.

(s) solid, (l) liquid, (g) gas