Chemical Changes

Question 1

What is a chemical change?

Answer 1

A change that results in the formation of one or more new substances.

Question 2

What are signs of a chemical change?

Answer 2

Color change, gas produced (bubbles), temperature change, light emitted, precipitate formed.

Question 3

Is rusting a chemical change? Why?

Answer 3

Yes, because iron reacts with oxygen to form a new substance (iron oxide).

Question 4

Is burning wood a chemical change?

Answer 4

Yes, it forms new substances like carbon dioxide and ash.

Question 5

Can chemical changes be easily reversed?

Answer 5

No, most are irreversible without further chemical reactions.

Question 6

What is a chemical reaction?

Answer 6

A process where atoms are rearranged to form new substances.

Question 7

What happens to atoms in a chemical change?

Answer 7

They are rearranged; no atoms are lost or gained.

Question 8

What is the difference between a chemical and a physical change?

Answer 8

Chemical changes form new substances; physical changes do not.

Question 9

Is cooking an egg a chemical change?

Answer 9

Yes, new substances are formed and the change cannot be reversed.

Question 10

Is dissolving sugar in water a chemical change?

Answer 10

No, it’s a physical change — no new substance is made.

Question 11

1

Answer 11

Q: What is a physical change?

Question 12

A: A change in appearance or state where no new substance is formed.

Question 13

Example: Melting ice, dissolving salt.

Answer 14

2

Question 15

A: A change that creates new substances with different properties.

Question 16

Example: Burning, rusting, neutralisation.

Answer 17

3

Question 18

A: They are rearranged but not changed chemically.

Answer 19

4

Question 20

A: Bonds between atoms are broken and new bonds form to make new substances.

Answer 21

5

Question 22

A: Physical — no new substance is formed.

Answer 23

6

Question 24

A: Physical — it changes state but remains H₂O.

Answer 25

7

Question 26

A: Chemical — it produces new substances like carbon dioxide and ash.

Answer 27

8

Question 28

A: It only changes state (liquid to gas), not the chemical identity.

Answer 29

9

Question 30

A: Yes — the food molecules are broken down and new substances are made.

Answer 31

10

Question 32

A: Yes — most physical changes are reversible.

Answer 33

11

Question 34

A: No — they often require another chemical reaction or are irreversible.

Answer 35

12

Question 36

A: Physical — it’s a state change (gas to liquid).

Answer 37

13

Question 38

A: Yes — a gas (CO₂) is produced and a new substance forms.

Answer 39

14

Question 40

A: Because no new substance is made and the salt can be recovered by evaporation.

Answer 41

15

Question 42

A: Temperature change, gas formation, colour change, or formation of a solid (precipitate).