What is a chemical equation?

A chemical equation is the symbolic representation of a chemical reaction in the form of symbols and formulae, wherein the reactant entities are given on the left-hand side and the product entities on the right-hand side.

How to balance a chemical equation?

What we are going to demonstrate below is the Algebraic Method or the Bottomley’s Method of balancing a chemical

For example, the following chemical equation can be considered for the purpose of demonstrating how to balance a chemical equation.

PCl5 + H2O –> H3PO4 + HCl

The first step is to assign arbitrary multipliers to each member substance of the equation.

a PCl5 + b H2O –> c H3PO4 + d HCl

Here, the objective is to ascertain the values of the arbitrary multipliers which make the chemical equation, balance. Hence the next step is to come up with linear equations of arbitrary multipliers by balancing the different elements of the two sides of the equation.

By balancing the element Phosphorus (P) –> a = c —-> equation (1)

By balancing the element Chlorine (Cl) –> 5a = d —–> equation (2)

By balancing the element Hydrogen (H) –> 2b = 3 c + d —–> equation (3)

By balancing the element Oxygen (O) –> b = 4c —–> equation (4)

Now we have 4 linear equations with 4 unknowns of a, b, c and d. The next step is to solve these 4 linear equations to find the 4 unknowns.

Since a = c, substituting c with a –>


2b = 3a + d

b = 4a

Since b = 4a, substituting b with 4a —>

5a = d

8a = 3a + d —> 5a = d

Lets assume a = 1

Then d=5, b=4 and c = 1

Finally the balanced chemical equation is as below.

PCl5 + 4 H2O –> H3PO4 + 5 HCl