Page 84 - SCERT Kerala State Syllabus 8th Standard Basic Science Textbooks English Medium Part 1_Neat

What kind of chemical reaction is the neutralisation reaction
between sodium hydroxide and hydrochloric acid?
Heat absorbing/Heat liberating

Find more examples of reactions from daily life which involves the
absorption or liberation of heat and record them in your science
diary.

Chemical reactions which liberate heat are called exothermic reactions
and those which absorb heat are called endothermic reactions.

Photochemical reactions
Glow of a fire fly
Photosynthesis is a chemical reaction that is responsible
for sustaining life on earth. In this reaction, plants
produce glucose by absorbing light. Note the chemical
equation of this reaction.
Water + Carbon dioxide + Light

Glucose + Oxygen
6H O + 6CO + Light C H O + 6O
2 2 6 12 6 2
The glucose thus formed is stored by plants in the form
of starch.

Light produced by a fire fly is the
Photosynthesis: An important result of a chemical reaction that
chemical reaction in the biosphere happens in its body. Light energy
is emitted as a result of the
Green plants are highly essential for
formation of oxyluciferin through
sustaining life on earth. Leaves are the food
the reaction between luciferin
factories of nature. In the presence of
and oxygen in the presence of
sunlight, chlorophyll in plants prepare
luciferase, an enzyme present in
glucose using carbon dioxide and water.
the fire fly’s body. This
This glucose is converted to starch and
phenomenon is known as
stored in the leaves, fruits and tubers of
plants. Green plants alone can prepare bioluminescence. 95% of the
glucose in this manner. energy liberated in this process
is in the form of light. This is the
reason why heat is not felt when
a fire fly glows.

Basic Science VIII 83