Page 87 - Chemistry_Form_2

Chemistry
for Secondary Schools

In principle, when writing molecular equations, the reactants and products should
be balanced.

Balancing chemical equations
All chemical equations must be written in accordance with the law of conservation
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of mass. This law states that, in a chemical reaction, the total mass of the products
equals the total mass of the reactants. This means, when balancing a chemical
equation, the number of each atom on both sides of the equation must be equal
because atoms do not varnish during a reaction, but are reorganised.

The following steps are followed when writing and balancing simple chemical
equations:

1. Write the equation in a word form.
2. Write the unbalanced equation including correct chemical formulas for
reactants and products.

3. List the number of atoms of each element on both sides of the equation.
4. Balance one element at a time. Usually start with metals or more complex
elements, and complete by balancing hydrogen and oxygen if present.
5. Use coefficients (whole numbers) to balance atoms. Never change subscripts
in a chemical formula.

6. Count atoms of all elements on both sides to make sure they are equal.
7. Simplify coefficients if necessary. The final equation should use the smallest
whole-number coefficients and should include the state symbols.

Example 4.1

Hydrogen chloride gas is formed when hydrogen gas burns in chlorine gas.
Write a balanced chemical equation for the reaction.
Step 1: Write the equation in word form

Step 2: Write the unbalanced chemical equation using symbols
The reactants are hydrogen gas (H ) and chlorine gas (Cl ), and the product is
2
2
hydrogen chloride gas (HCl):

80 Student’s Book Form Two

01/08/2025 11:20:57
CHEMISTRY FORM TWO NEW 2025 DUMMY.indd 80
CHEMISTRY FORM TWO NEW 2025 DUMMY.indd 80 01/08/2025 11:20:57