Page 95 - Chemistry_Form_2

Chemistry
for Secondary Schools

Another example of a combination reaction is the reaction between lead(IV)
oxide and sulfur dioxide. If lead(IV) oxide is slightly heated and then lowered
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into a gas jar of sulfur dioxide, the two compounds combine to form one new
compound, lead(II) sulfate.

Combination reactions play crucial roles in various biological, environmental,
and industrial processes. Some of these processes include:

(a) Formation of water: Formation of water relates to the combination reaction
whereby hydrogen and oxygen gases combine to form water as shown in the
following reaction:

(b) Rusting of iron: Rusting is a slow chemical process in which iron reacts with
oxygen and water to form hydrated iron(III) oxide (rust). It is an example
of a combination reaction and a type of corrosion that weakens iron objects
over time. The chemical reaction for rusting is:

The iron hydroxide (Fe(OH) ) further transforms to a more stable form,
3
hydrated iron(III) oxide which is reddish-brown (rust).

Rusting is a major issue in construction, transportation, and machinery,
leading to structural damage and economic losses.

(c) Formation of calcium hydroxide (slaked lime): Calcium oxide (quick lime)
reacts with water to form calcium hydroxide (slaked lime) an essential material
in construction that is frequently used for setting cement and plaster. The
reaction equation is:

(d) Photosynthesis: In plants, carbon dioxide gas combines with water in the
presence of sunlight to form glucose and oxygen.

88 Student’s Book Form Two

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CHEMISTRY FORM TWO NEW 2025 DUMMY.indd 88