Class seven Science Chapter 6 Additional Questions
Chapter 6: Physical and Chemical changes
Fill in the blanks:
1. Photosynthesis is a——— change.
2. A chemical change is a———- change.
3.——–, nickel and———– are used to make stainless steel.
4. Beautiful snowflake is formed by the process of—————-.
5. The iron sheets used to make buckets, drums, sheds (roof) are——– to prevent rusting.
Answers: 1. chemical 2. Permanent 3. Chromium, manganese 4. crystallization 5. galvanized
Match the following:
Answers: i. b ii. a iii. d iv. C
Very Short Answer Type Questions
1. What is rusting?
Answer: Oxidation of iron surface in the presence of air and moisture is called rusting.
2. Define physical change.
Answer: A physical change occurs when a substance simply changes its physical properties, such as the shape, size, colour, or state of the substance without any new substance being created.
3. Which process is used to obtain large crystals from the solution of pure substance?
Answer: Crystallisation is used to obtain large crystals from the solution of pure substance.
4. What do you mean by chemical change?
Answer: Changes that lead to the formation of new substances with different chemical properties are referred to as chemical changes.
5. What are the factors responsible for rusting of iron?
Answer: Air and moisture are responsible for the rusting of iron.
6. Write the chemical formula of iron oxide.
Answer: The chemical formula of iron oxide is Fe2O3.
7. Write the chemical formula of magnesium hydroxide
Answer: The chemical formula of magnesium hydroxide is Mg (OH)2.
8. Give one example of physical change.
Answer: Tearing of paper is a physical change.
9. What are the materials used to convert the iron into stainless steel?
Answer: Manganese, chromium and nickel are used to convert the iron into stainless steel.
10. Define galvanization.
Answer: It is the process of depositing a thin layer of zinc metal on iron objects. This includes zinc covering the iron, usually in the form of paint.
Short Answer Type Questions
1. Write any four characteristics of chemical changes.
Answer: The characteristics of chemical change are as follows:
(1) In a chemical change, one or more new substances are formed.
(2) A chemical change is a permanent change that cannot normally be reversed. This means it’s irreversible.
(3) Energy may be absorbed or emitted in the form of heat, light or any sort of radiation during a chemical reaction.
(4) In a chemical change, sound may be produced.
2. Mention the characteristics of physical change.
Answer: The characteristics of physical change are as follows:
(1) In a physical change, no new substance is formed.
(2) Such changes take place only in any substance’s physical properties.
(3) All changes in this classification are usually reversible, while cutting of paper, wood or any substance is an irreversible change.
3. Blowing a balloon is a physical change. Give a reason for your answer.
Answer: While blowing a balloon, the balloon expands in size, i.e. the change takes place in the size and shape of the balloon. However, if we remove all the air from the balloon, it comes back in its original position. Therefore, it is an example of physical change.
4. What will happen when we burn a strip of magnesium? Is it a chemical change/ physical change?
Answer: When burning a strip of magnesium, it emits a bright white light and powdery ash is left behind after burning. Ash is a new substance produced after reacting with oxygen. The following formula will represent this change:
It is a chemical change.