Question

1. You forget a toast in toaster and it turns black. Can this change be reversed?

2. You blow dry your wet hair, How can you reverse this change?

3. Why is cooking of food an irreversible change?

4 Give an example of a physical change that cannot be reversed.

5. What kind of change is observed when copper utensils appear to be greenish in
colour?

6 Which of these changes can be reversed: grain to flour, bud to flower, melting of
ghee and ripening of fruits?

7 Define the following:
a. Reversible change
b. Physical change
c. Irreversible change
d. Chemical change
G. Answer the following questions in detail.

1. Explain with the help of examples, the difference between the changes that can be
reversed and those that cannot be reversed.

2. Explain the type of changes involved in this sequence
lce cube placed in sun —— puddle of water — disappearance of puddle

3. What are physical changes? Give two examples.

4. Why is getting a new hair cut considered to be a physical change?

5 What do you observe when fireworks explode? Is anything new formed? What type
of change is it?

6. Squeezing oranges for juice is a physical change. Justify.

7 Why does the idli batter rise when kept overnight without refrigeration?

8. Places such as the mountains, where temperatures get very low during winters, the
plastic pipes meant for water transportation break. Why do you think it happens?

9. Differentiate between:
a, reversible and irreversible changes
b. physical and chemical changes
c evaporation and condensation
d. expansion and contraction

10. Look at the following pictures and write down as to whether the changes are
reversible or irreversible. For reversible changes, draw a second arrow below the
first in the opposite direction.​

Answer 1

Explanation:

1)chemical

2)we can reverse it by again wetting our hair

3)because it can't become raw again

4)dissisipation

5)chemical

6)irreversible, irreversible , reversible , irreversible

7)I've told below

8) told below

9)melting , evaporation

10)physical change are which cant be reversed for eg drying of clothes , drying of wet hair

11)it is considered as physical chande because hair grows again

12)firework exploding is a chemical change as it cant be reversed and new product co2 is formed

13)it is a chemical change because no. new substance is formed

14)idli batter rises because of process of fermentation

15)this is because freezing and expansion of water exerts pressure from inside hence they break

16)reversible - this type of change in which substance can be changed again to its original form

irreversible - in this change substance cant be changed to its original form

chemical - in it substance property changes and new product is formed it is irreversible

physical - substance property does not changes no new product formed reversible change

evaporation - in this water changes into water vapour when it heats

condensation - in this water cools from vapour to water again

expansion - when a body volume increase on heating

contraction - when body volume decrease on cooling or forms its original shape

17) not clear

mark me as brainliest hope it helps you !!

Answer 2

Answer:

1. A toast in a toaster becomes black. this is an irreversible change.
2. A toast in a toaster becomes black. this is an irreversible change.It's a physical change because when blow drying your hair,no new substance is made.
3. A toast in a toaster becomes black. this is an irreversible change.It's a physical change because when blow drying your hair,no new substance is made.When we heat raw food materials, we get cooked food. The cooked food cannot be converted back into raw food. So, the cooking of food is an irreversible change
4. A toast in a toaster becomes black. this is an irreversible change.It's a physical change because when blow drying your hair,no new substance is made.When we heat raw food materials, we get cooked food. The cooked food cannot be converted back into raw food. So, the cooking of food is an irreversible changeMany physical changes can be reversed, like water freezing to form ice. But some physical changes cannot, such as an egg being cracked or wood being ground into sawdust.
5. When a copper utensil is exposed to air or comes in contact with the same, a reaction takes place between copper,and gases and moisture present in the air which results in the formation of a mixture of copper compounds which imparts a green colour to the surface of the metal.
6. Melting of ghee can be reversed because it is our physical change or reversible change.
7. (i) a change in which the original substance can be recovered.

(ii) a change in which the physical properties of a substance changes.

(iii) a change in which the original substance cannot be recovered.

(iv) a change that produces entirely new substances with different chemical properties.

____________the end ____________

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