Burning

Q.

How is sand useful for extinguishing fire?

1. It limits the supply of oxygen.

2. It limits the supply of oxygen and it smothers the fire.

3. It smother the fire.

4. Sand is flammable.

Q. Which of these changes does a burning matchstick undergo?
(i) Endothermic reaction
(ii) Exothermic reaction
(iii) Chemical change

1. Only (i) and (ii)
2. Only (ii) and (iii)
3. Only (i) and (iii)
4. (i), (ii) and (iii)

Q.

Mention two physical changes that occur in the kitchen.

Q.

Liquid changes into solid on cooling but the batter of a cake changes into a cake on heating in an oven. Why?

Q. When you burn petrol, flames appear. What is the type of reaction?

1. An endothermic reaction
2. An exothermic reaction
3. A physical change
4. A reversible reaction

Q. Which among the following is a reversible change?

1. Formation of curd
2. Baking bread
3. Making popsicles
4. Cutting a tree

Q.

7. Give one word:

2. Is melting of wax reversible or irreversible change?

Q.

Give an example to explain the difference between changes that can or cannot be reversed.

Q.

10. Which is a way to make a change happen?

1. Heating of substance

2. Mixing of substance with another substance

3. Cooling of substance

4. All of the above

Q.

8. Which of the steps while burning a candle is not reversible?

1. Melting of solid wax

2. Wax vapour burn into flame

3. Liquid wax changes into vapours

4. All of the above

Q.

On lightning the candle, the candle burns and gives off light. Which of the following statement(s) about it is/are incorrect?

1. Burning of a candle is an irreversible change.

2. Melting of the candle wax is a reversible change.

3. Burning of a candle is a reversible change.

4. Melting of the candle wax is an irreversible change.

Q.

A change can be reversible and irreversible at the same time.

1. True
2. False

Q.

State whether the change can be reversed or not.

Souring of milk.

Q. Boojho’s sister broke a white dove, a symbol of peace, made of Plaster of Paris (POP). Boojho tried to reconstruct the toy by making a powder of the broken pieces and then making a paste by mixing water. Will he be successful in his effort? Justify your answer.​

Q.

2. State whether this change can be reversed or not.

(d) Baking cake in an oven.

Q.

A type of change that can be returned to its original form by reversing the conditions?

Q.

A potter working on his wheel, shaped a lump of clay into a pot. He then baked the pot in an oven. Do these two acts lead to the same kind of changes or different? Give your opinion and justify your answer.

Q.

Question 8

Look at the figures given below, which show three situations (a) burning candle (b) an extinguished candle (c) melting wax.
Which of these shows a reversible change and why?

Q. Which of the following changes is reversible?

1. Cutting of wood
2. Ripening of fruit
3. Molding of clay
4. Making chapati

Q.

Which among the following is an example of an irreversible change?

1. Making structures of sand on beach

2. Melting of ice

3. Cutting trees

4. Making paper planes

Q.

Which of the following are physical changes?

a) Rusting of an iron sheet

b) Cutting of an iron rod

c) Melting of ghee

d) Breaking water into hydrogen and oxygen

e) Diluting an acid solution

Q.

Give a reason for the following statement.

The curdling of milk is an irreversible change.

Q.

1. Why is curd formation an irreversible change?

Q. A piece of iron is heated till it becomes red-hot. It then becomes soft and is beaten to the desired shape. What kind of changes are observed in this process– reversible or irreversible?

Q.

Question 12

Which of the following changes cannot be reversed?
Blowing of a ballon
Folding a paper to make a toy aeroplane
Rolling a ball of dough to make roti
Baking cake in an oven
Drying a wet cloth
Making biogas from cow dung
Burning of a candle

Q. Burning of a matchstick is :

1. Endothermic reaction
2. Exothermic reaction
3. Decomposition reaction
4. Molecular reaction

Q. The burning of paper is a reversible change.

1. True

2. False

Q. Melting of a candy bar is an irreversible change.

1. True
2. False

Q.

12. When does the ice melts? Is it reversible ?

Q. The general day to day activities of a primary school going teen named Swami are mentioned below.
1. To walk through a waterlogged area, Swami shortens the length of his dress by folding it.
2. In school, he drew an apple in his slate with chalk.
3. After school, he came directly came back to his home and started playing with his new toy, but accidently it broke.
4. At night, his mother cooked food for him. He ate and then retires to bed.
Connect the above excerpts to reversible or irreversible change.

1. Reversible change - 1, 2, 3, 4; Irreversible change - NA

2. Reversible change - 3, 4; Irreversible change - 1, 2

3. Reversible change - NA; Irreversible change - 1, 2, 3, 4

4. Reversible change - 1, 2; Irreversible change - 3, 4