Page 87 - SCERT Kerala State Syllabus 8th Standard Basic Science Textbooks English Medium Part 1_Neat

Switch + - known as electroplating. Electroplating is
an electrochemical reaction.
Observe the figure which shows the
arrangement of coating silver on an iron
ring (Figure 6.8).

The silver rod and the iron ring are
connected to the battery as shown in the
Iron ring
figure. When switched on, the iron ring
gets covered with a thin layer of silver
metal. If copper is to be coated, copper
Silver rod
sulphate solution and a copper rod
A mixture of silver
cyanide and sodium instead of silver rod should be used.
cyanide solutions.
Now, you might have understood that
Fig. 6.8
forms of energy like heat, light and electricity are exchanged during
chemical reactions. There are chemical reactions which involve the
absorption or liberation of energy. Those which absorb energy are
known as endoergic reactions and those which liberate energy are
known as exoergic reactions.
List the energy involved in the chemical reactions discussed above
and record them in your science diary.

Chemical change Major energy change

Reaction between magnesium and hydrochloric acid Heat energy is liberated

Table 6.2
Energy transfer occurs during any chemical reaction. A chemical
reaction will be known based on the major energy form which
See 'Vaidyuthalepanam' gets absorbed or liberated.
in School Resources in
IT@School Edubuntu Identify and tabulate the class of chemical reactions with which
you have already familiarised yourselves.

Reaction Name of chemical reaction

Heating potassium permanganate Exothermic reaction

Table 6.3
86 Basic Science VIII