STD-6, CHAPTER-5: CHANGES AROUND US, EXERCISE QUESTION ANSWERS

 A.     FILL IN THE BLANKS.

1.      All irreversible changes bring a ______ change in a substance.

Ans: permanent

2.      A change, in which the substance produced can get back to the original form, is called a ______ change.

Ans: reversible

3.      Bending of an iron rod is a ______ change.

Ans: physical

4.      Burning of fuel is a _______ chemical change, whereas rusting of iron is a ______ chemical change.

Ans: fast, slow

5.      In chemical change, new substances with ______ properties are formed.

Ans: different

B.      WRITE TRUE OR FALSE FOR THE FOLLOWING STATEMENTS.

 

1.      Glowing of an electric bulb is a fast change - TRUE

2.      Deforestation is a reversible change. - FALSE

3.      Burning of paper is a temporary change. - FALSE

4.      Cutting of an apple is a chemical change. - FALSE

5.      Making of fruit salad is a chemical change. - FALSE

6.      Changing milk into curd is a physical change. - FALSE

 

C.      TICK THE CORRECT OPTION.

 

1.      Which of the following can be considered as a fast change?

(a)    Growth of a child

(b)   Germination of seeds

(c)    Bursting of a fire cracker

(d)   Cooking of food      

      Ans: bursting of a fire cracker

2.      Evaporation of water is a-

(a)   Physical change

(b)   Fast change

(c)    Irreversible change

(d)   Chemical change            

      Ans: Physical change

3.      Which one of these changes is a reversible change?  

(a)   Burning of a candle

(b)   Inflating a balloon

(c)    Baking of chappati

(d)   Grinding of wheat grains into flour      

       Ans: inflating a balloon

4.      Which one of these is an irreversible change?

(a)   Growth of a child

(b)   Stretching a rubber band

(c)    Evaporation of water

(d)   Formation of ice from water

      Ans: growth of a child

5.      A piece of paper undergoes a chemical change, when it is-

(a)   cut

(b)   folded

(c)    reshaped into a paper toy

(d)   burned

      Ans: burned

D.     ANSWER THE FOLLOWING QUESTIONS IN BRIEF.

1.      Define the following terms.

(a)   Reversible change

(b)   Chemical change

(c)    Physical change

Ans: a) Reversible Change: a change, in which substance produced, can be brought back into its original form is called as a reversible change.

b) Chemical change: a change, in which a new substance is formed is called as a chemical change.

c) Physical change: a change, in which no new substance is formed is called a physical change.

2.      Distinguish between fast and slow changes. Give two examples of each type.

Ans: Fast change: A change that takes place in a shorter duration of time is called a fast change. Example: bursting of a balloon, lighting of a bulb

Slow Change: A change that takes place over a longer duration of time, is called a slow change.

Example: change of seasons, growth of a plant

3.      Give two examples each of reversible and irreversible change.

Ans: Reversible Change: stretching a rubber band, evaporation of water

Irreversible Change: Baking of chappati, growth of a child

4.      State some of the irreversible biological changes that take place in nature.

Ans: Some of the irreversible biological changes that take place in nature are,

i) germination of a seed

ii) growth of animals

iii) forest fire

iv) burning of fuels

5.      Give one example of a physical change in which (i) energy is given out, (ii) energy is absorbed.

Ans: (i) Energy is given out during burning of a fuel

(ii) Energy is absorbed during boiling of water

E.      ANSWER THE FOLLOWING QUESTIONS.

 

1.      Give two differences between reversible and irreversible changes.

Ans: Reversible Change: i) A change, in which substance produced, can be brought back into its original form, is called as a reversible change.

ii) These are temporary changes.

Examples: stretching a rubber band, evaporation of water

Irreversible Change: i) A change, in which the substance produced cannot get back to the original form, is called an irreversible change.

ii) These are permanent changes.

Examples: Baking of chappati, growth of a child

2.      ‘Formation of curd is an irreversible as well as a chemical change.’ Justify this statement.

Ans: i) Milk is a liquid. After curdling, it changes into a semi-solid material which has a different taste. As, a new substance is formed, the formation of curd is a chemical change.

ii) Again, the process cannot be reversed and we cannot get back milk from curd. So, it is also an irreversible change.

3.      Water cycle is a natural change. Classify it as a (i) physical or chemical change,  (ii) a reversible or irreversible change. Also, justify your answer.

Ans: Water cycle is a natural change. In this cycle, water changes its states due to difference in temperature. 

i) It is a physical change. Because in this cycle no new substance is formed. Water only changes its state.

ii) It is a reversible change as we can get back the original substance by changing temperature. For example, liquid water changes into water vapour on heating and the same water vapour again changes into liquid form on cooling.

4.      How can we say that burning of candle is a chemical change but the glowing of bulb is a physical change?

Ans: i) After burning the candle produces smoke and the thread in the candle changes into ash. Thus new substances are formed. So we can say that burning of candle is a chemical change.

       ii) When the switch is on, the electric bulb starts glowing. And when it is switched off it          stops glowing. No new substance is formed. So, it is a physical change.