The City School
PECHS Junior Boys
Revision worksheet
Science Grade: 7
Topics: Reversible and irreversible changes.
Objective
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Q1. Encircle the correct answers.
i)
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Changes of state are _____________
a. irreversible
b. reversible
c. permanent
ii)
_______________ is needed to start a material burning.
a. carbon dioxide
b. oxygen
c. heat.
iii)
In _________ changes, the original materials can be recovered back easily.
a. irreversible
b. small
c. reversible.
Q2. Fill in the blanks with appropriate answers.
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i)
____________________ gas is formed when a material burns.
ii)
A lot of energy in the form of ______________ and _____________
are given out in the process of burning.
iii)
Substances that catches fire easily and burn rapidly in the air are called
___________________.
Q3. Write true or false for the following statement. If statement is false write the
correct statement.
i)
Heat can bring about both reversible and irreversible changes.
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(
)
___________________________________________________
___________________________________________________
ii)
Burning of candle is irreversible change.
(
)
___________________________________________________
___________________________________________________
Subjective
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Q4. Give scientific reasons for the following statements.
i)
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An astronaut can not lit a candle on moon.
Reason: _______________________________________________________
______________________________________________________________
______________________________________________________________
ii)
To carry out an investigation we can change only one variable.
Reason: _______________________________________________________
______________________________________________________________
______________________________________________________________
Q6. Mr. Ali observes the following changes after conducting an investigation. Separate
the changes brought about by heating and changes brought by mixing and write in
the respective column. Also decide whether the change is reversible or irreversible.
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a)
b)
Egg shell in vinegar.
Burning a candle.
Change
Brought about by
heating or mixing
Rusting a nail
Reversible or
irreversible.
a
b
c
Q8. ‘Decomposition of sugar is an irreversible change.’
a. Justify the statement with a reasons. _____________________
b. Sugar decomposes into: _______________________________
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