Tick the correct type of change corresponding to the following processes. Process Physical change Chemical change Evaporation of perfume on your skin Burning of sugar Melting of copper metal Tearing a piece of aluminium foil Fermentation Condensation Sublimation

Process Physical change Chemical change Evaporation of perfume on your skin Evaporation is the process of conversion of liquid into gas. No new substances are formed during this change, hence it is a physical change. Process Physical change Chemical change Burning of sugar Burning of sugar releases carbon dioxide and other new substances that cannot be converted back to sugar. Therefore, the burning of sugar is a chemical change. Process Physical change Chemical change Melting of copper metal When copper metal is melted, solid metal turns into liquid. It can be converted back to solid state by cooling. Since the change is reversible and no new substances are formed it is a physical change. Process Physical change Chemical change Tearing a piece of aluminium foil Tearing of aluminium foil does not form any new substances, only shape and size of the foil changes. Therefore, it is a physical change. Process Physical change Chemical change Fermentation Fermentation is the process of break down of a compound into simple substances in presence of bacteria. New substances are formed in this reaction. Therefore, fermentation is a chemical change. Process Physical change Chemical change Condensation Condensation is the process of conversion of liquid into solid by cooling. No new substances will be formed during this change, hence it is a physical change. Process Physical change Chemical change Sublimation Solids will be converted to gases directly in this change, since it does not form any new substance and therefore it is a physical change.

E M B I B E

WOW! SCIENCE Hands-on Learning in SCIENCE 7>Chapter 7 - Chemical Changes and Reactions>EVALUATE>Q 1

HARD

7th CBSE

IMPORTANT

Earn 100

You must have seen that the silver articles, such as silver jewellery, turn black after sometimes. Explain this process. Is it a physical or a chemical change? What can be done to clean the silver articles?

Important Questions on Chemical Changes and Reactions

MEDIUM

7th CBSE

IMPORTANT

WOW! SCIENCE Hands-on Learning in SCIENCE 7>Chapter 7 - Chemical Changes and Reactions>EVALUATE>Q 2

Explain why the following is an example of a chemical change:

Photosynthesis.

MEDIUM

7th CBSE

IMPORTANT

WOW! SCIENCE Hands-on Learning in SCIENCE 7>Chapter 7 - Chemical Changes and Reactions>EVALUATE>Q 2

Explain why the following is the example of a chemical change:

Rotting of an egg.

HARD

7th CBSE

IMPORTANT

WOW! SCIENCE Hands-on Learning in SCIENCE 7>Chapter 7 - Chemical Changes and Reactions>EVALUATE>Q a)

Identify the type of chemical reaction given below for a chemical equation:

A g N O_{3} + K C l \to A g C l (↓) + K N O_{3}

HARD

7th CBSE

IMPORTANT

WOW! SCIENCE Hands-on Learning in SCIENCE 7>Chapter 7 - Chemical Changes and Reactions>WORKSHEET>Q A

Solve the crossword puzzle.

ACROSS

1. Substances that undergo chemical reactions

4. Reaction between acids and bases are called

5. Reaction of silver nitrate and potassium iodide is an example of this type of reaction

6. heat is absorbed in this type of reaction

DOWN

2. The technique used to obtain pure substances from the solution

3. This type of change is usually permanent and irreversible

Question Image

HARD

7th CBSE

IMPORTANT

WOW! SCIENCE Hands-on Learning in SCIENCE 7>Chapter 7 - Chemical Changes and Reactions>WORKSHEET>Q B

Tick the correct type of change corresponding to the following processes.

Process	Physical change	Chemical change
Evaporation of perfume on your skin
Burning of sugar
Melting of copper metal
Tearing a piece of aluminium foil
Fermentation
Condensation
Sublimation

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