Page 96 - Chemistry_Form_2

Chemistry
for Secondary Schools

(e) Formation (synthesis) of ammonia: In industry, ammonia gas is manufactured
from a combination reaction between nitrogen and hydrogen gases as
represented in the following reaction:
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Decomposition reactions
A decomposition reaction is a chemical reaction in which a compound breaks
down (decomposes) into its components. This reaction can be expressed in the
form of:

The decomposition reaction is the opposite of a combination reaction. Generally,
decomposition reactions are classified into three main types, namely catalytic,
electrolytic and thermal reactions. In a catalytic decomposition reaction, an agent
called a catalyst is introduced that alters the rate of a chemical reaction but remains

unchanged at the end of the reaction. For example, potassium chlorate readily
decomposes when heated in the presence of manganese(IV) oxide (catalyst) to
produce oxygen gas and potassium chloride.

An electrolytic decomposition reaction is achieved by exposing an aqueous
solution or molten compound to an electric current. An example of an electrolytic
decomposition reaction is the electrolysis of water, which is represented by the
following chemical equation:

Thermal decomposition occurs when a compound is exposed to direct heat or
radiation. For example, when lead(II) nitrate crystals are heated, they decompose
with a cracking sound to produce lead(II) oxide, nitrogen dioxide gas, and oxygen
gas.

Student’s Book Form Two 89

01/08/2025 11:20:59
CHEMISTRY FORM TWO NEW 2025 DUMMY.indd 89
CHEMISTRY FORM TWO NEW 2025 DUMMY.indd 89 01/08/2025 11:20:59