Chemical changes involve breaking of old chemical bonds which exist between the atoms of reacting substances and then making new chemical bonds between the rearranged atoms to form new substances.
True
False
A chemical change is temporary and reversible.
True
False
When copper objects are left exposed to moist air, a brown flaky layer develops on their surface.
True
False
During melting, the temperature keeps changing.
True
False
Cooking of food is a change in which energy is absorbed.
True
False
Folding of paper is a chemical change.
True
False
A change in which heat is absorbed is called an exothermic change.
True
False
A physical change is permanent and irreversible.
True
False
Respiration helps us to release energy needed by the cells of the body.
True
False
The rate of evaporation decreases with the increase in temperature.
True
False
Sublimation is the process in which a solid directly changes into its vapour on heating without passing through the liquid state.
True
False
Click the correct answer.
Which of the following is a desirable change?
Rusting of iron
Ripening of fruits
Rotting of fruits
Curdling of milk meant for drinking
Which of the following is an irreversible change?
Melting of ice
Folding of paper
Stretching of a rubber band
Burning of a candle
Which of the following changes involves absorption of heat?
Burning of a candle
Burning of fuels
Cooking of food
Burning of crackers
Which of the following is not a characteristic of a chemical change?
A chemical change is temporary and can be reversed.
A chemical change involves formation of one or more new substances.
There is a change in the net energy of the system during a chemical change.
There is a change in the mass of the substance undergoing a chemical change.
Which of the following confirms you that a chemical change has not occurred?
When evolution of gas has occurred
When colour of the substance changes
When precipitate is formed
When chemical composition does not change
In which of the following processes, vapour on cooling changes into a liquid?
Melting
Freezing
Condensation
Evaporation
Click each box on the left and then click the matching box on the right.
Match the columns.
Curdling of milk
Rotting of fruits
Dissolving
Rusting
Evaporation
Desirable change
Undesirable change
Physical change
Chemical change
Surface phenomenon
Click the correct answer.
A physical change is temporary and
.
cannot be reversed
cannot be changed
can be reversed
permanent
Germination of a seed is a
change.
chemical
physical
temporary
reversible
There is a change in the net
of the system during a chemical change.
body
weight
mass
energy
During a
change, a substance undergoes a change in its physical properties without any change in its composition.
chemical
physical
logical
composite
Burning is a
change.
chemical
physical
reversible
temporary
The rate of evaporation
with increase in temperature.
decreases
falls
increases
lowers
The process in which a solid directly changes into vapour on heating without passing through the liquid state is called
.
