Page 31 - ICSE Chemistry 8

REVERSIBLE AND IRREVERSIBLE CHANGES

Changes in which we can get back the original
substance by reversing the ac on are called
reversible changes. For example, mel ng of ice
and freezing of water, change in shape and size
of a balloon on blowing air in it, adding sugar to
water and separa ng sugar from water by hea ng,
and folding and unfolding of paper are reversible
blowing air in a balloon baking of chapatti
changes.
Fig. 2.2: Reversible and irreversible changes
Changes in which we cannot get back the original
substance by reversing the ac on are called irreversible changes. For example, burs ng of balloon, cu ng
of paper and baking of chapa from dough are irreversible changes.

Activity 2.1

Aim: To write fi ve examples of reversible changes and fi ve examples of irreversible changes
Write fi ve examples of reversible changes and fi ve examples of irreversible changes in your scrapbook.
Paste related pictures.

PERIODIC AND NON-PERIODIC CHANGES

Changes that repeat themselves a er a
regular interval of me and are bound to
happen are called periodic changes. For
example, rising and se ng of the sun,
changing of seasons and phases of the
moon are periodic changes.
Changes that do not repeat a er a regular
rising of the sun precipitation
interval of me, i.e., occur irregularly
Fig. 2.3: Periodic and non-periodic changes
are called non-periodic changes. For
example, precipita on, earthquake and wil ng of a plant are some non-periodic changes.

DESIRABLE AND UNDESIRABLE CHANGES

Changes that are benefi cial to us are called desirable changes. For example, ripening of fruits, burning of
fuels to run automobiles and cooking of food are desirable changes.

Changes that are not benefi cial and may bring harm to us are called undesirable changes. For example,
occurrence of earthquakes and fl oods, rus ng of iron and spoilage of food are undesirable changes.

SLOW AND FAST CHANGES

Changes that take place over a long period of me are called slow changes. These changes may take
hours, days, months or even years to occur. For example, curdling of milk, growth of plants, changing of
day into night and rus ng of iron are slow changes.

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