Balancing Chemical Equations:

When we write the chemical reaction we have to keep in mind that matter is neither created nor destroyed. 

This means the number of atoms on both sides of equation should be the same.

In general, we can balance a chemical equation by the following steps:

1. Identify all reactants and products and write them correct.

2. Begin balancing the equation by trying different coefficients (numbers written before formula) to make the number of atoms of each element the same on both sides of the equation.

3. First, we try coefficients to balance the element that appeared only once on each side of the equation (the formulas containing these elements must have the same coefficient).

Next, balance the elements that appear only once on each side of the equation but in unequal numbers of atoms.

Finally, balance elements that appear in two or more formulas on the same side of the equation.

4. Check your balanced equation to be sure that total number of atoms on both sides are the same on both sides of equation.

For example, the producing of oxygen for heating potassium chlorate (KClO₃).

KClO₃ → KCl + O₃

All three elements (K, Cl, and O) appear only once on each side of the equation, but only for K and Cl  have equal numbers of atoms on both sides. Thus, KClO₃ and KCl must have the same coefficient.

The next step is balance the O atoms, because there are three O atoms on the left and two O atoms on the right of the equation, we can balance the O atoms by placing a 2 in front of KClO₃ and a 3 in front of O₂:

2KClO₃ → KCl + 3O₃

Finally, we balance the K and Cl atoms by multiplying the same coefficient on both sides "2":

2KClO₃ → 2KCl + 3O₃

For final check,

Number of K atoms on the reactants = products = 2

Number of Cl atoms on the reactants = products = 2

Number of O atoms on the reactants = products = 6

Now let us consider the combustion of the natural gas component ethane (C₂H₆) in presence of  oxygen or air to yield carbon dioxide (CO₂) and water. The unbalanced equation is

C₂H₆ + O₂ → CO₂ + H₂O

First, we look at the elements that appeared only once on each side of the equation (C and H).

To balance the C atoms, we place a 2 in front of CO₂:

C₂H₆ + O₂ → 2CO₂ + H₂O

To balance the H atoms, we place a 3 in front of H₂O:

C₂H₆ + O₂ → 2CO₂ + 3H₂O

To balance O atoms we multiply left hand side of the equation by the number of atoms on the right hand side of the equation and divide over the number of atoms on the left hand side of the equation (meaning we multiply by 7 and divide by 2).

C₂H₆ + 7/2 O₂ → 2CO₂ + 3H₂O

However, we normally prefer to express the coefficients as whole numbers. Therefore, we multiply the entire equation by 2 to convert 7/2 to 7:

2C₂H₆ +7 O₂ → 4CO₂ + 6H₂O

For final check,

Number of C atoms on the reactants = products = 4

Number of H atoms on the reactants = products = 12

Number of O atoms on the reactants = products = 14